Endocrinology Exam Domains 2026: Complete Guide to All 18 Content Areas

Overview: What the AOBIM Endocrinology Content Outline Covers

The American Osteopathic Board of Internal Medicine (AOBIM) organizes its initial Endocrinology subspecialty written examination around 18 official content areas, each assigned a percentage range rather than a fixed weight. That distinction matters: instead of memorizing "domain X equals exactly 8%," candidates should think in ranges, because the board reserves flexibility to shift a few points between closely related areas from one testing cycle to the next.

This guide breaks down every one of the 18 domains, explains why some carry far more weight than others, and shows how to allocate limited study time accordingly. If you're still mapping out your overall preparation strategy, pair this domain breakdown with our companion Endocrinology Study Guide 2026, which walks through a full first-attempt preparation plan.

All 18 Content Domains and Their Percentage Ranges

Below is the complete AOBIM content outline for the initial Endocrinology subspecialty examination. These ranges are the foundation for every study plan you build.

Notice the pattern: one domain dominates, six domains sit in a solid mid-tier band, and the remaining eleven fill out the rest of the exam in smaller but still meaningful proportions. Understanding this hierarchy is the entire point of studying the outline before you study the medicine.

High-Yield Domains: Where to Concentrate Your Study Hours

Because diabetes mellitus alone can represent roughly one in every seven or eight questions, it deserves proportionally more repetition, more practice questions, and more review passes than any other domain. Candidates who under-invest here often find their overall score suffers even if they perform well elsewhere.

Mid-Weight Domains: Steady, Reliable Points

A second tier of domains - Principles of endocrinology/hormones/physiology (4-8%), Disorders of the ovaries/breast (3-7%), and several 2-6% domains including Lipid disorders, Disorders of the testes, Polyglandular/Multiple-Organ syndromes, and Bone/Osteoporosis - round out a meaningful share of the question bank.

Lower-Weighted but Still Testable Domains

Eight domains sit at 1-5%: Hypoglycemic syndromes/Islet cell disorders, Tumors of the thyroid, Menstrual cycle/Fertility/Contraception, Disorders of the adrenal medulla/Tumors of adrenal, Obesity, and Miscellaneous. Individually small, but collectively these lower-weighted domains can still account for a meaningful chunk of total questions.

• Domain 3 - Hypoglycemic syndromes/Islet cell disorders: insulinoma workup, factitious hypoglycemia, and non-diabetic hypoglycemia differentials.
• Domain 7 - Tumors of the thyroid: nodule risk stratification, biopsy indications, and differentiated versus medullary thyroid cancer management basics.
• Domain 9 - Menstrual cycle/Fertility/Contraception: hypothalamic amenorrhea, hyperprolactinemia effects on cycling, and contraceptive hormone interactions.
• Domain 12 - Adrenal medulla/adrenal tumors: pheochromocytoma biochemical testing and incidentaloma management.
• Domain 14 - Polyglandular/Multiple-Organ syndromes: autoimmune polyglandular syndromes and MEN syndromes.
• Domain 15 - Obesity: pharmacologic and physiologic management principles.
• Domain 18 - Miscellaneous: topics that don't cleanly fit elsewhere in the outline, often testing integrative clinical reasoning.

Don't treat this tier as optional. A candidate who skips all eight low-weight domains could be walking away from a substantial number of missed points across the full exam. For a broader sense of how domain coverage interacts with overall exam difficulty, see How Hard Is the Endocrinology Exam? Complete Difficulty Guide 2026.

How Domains Translate Into 300 Questions Over Seven Hours

The initial AOBIM Endocrinology subspecialty examination consists of 300 multiple-choice questions administered over seven hours. There is no separate breakdown published per domain on test day - the percentage ranges describe the outline used to build the exam, not a fixed count you'll see question-by-question. That said, using the midpoint of each range gives a reasonable planning estimate of how many questions to expect from each area.

Because the exam is long and single-day, pacing across domains matters as much as content mastery. With 300 items in seven hours, you have roughly a minute and a half per question on average - tight enough that you cannot afford to get bogged down on any single low-weight topic at the expense of high-yield domains like diabetes mellitus or the thyroid/adrenal/pituitary/parathyroid cluster.

Mapping Domains Onto a Study Timeline

Once you understand the weight distribution, the next step is sequencing. A domain-aware timeline front-loads the heaviest content areas while still reserving dedicated time for every low-weight domain before test day.

This is a structural framework, not a rigid formula - adjust based on your fellowship exposure and personal weak spots. For a more detailed week-by-week methodology including practice-question rotation and review cadence, the Endocrinology Study Guide 2026 goes deeper into technique.

Registration, Fees, and Eligibility Reminders

Domain mastery only matters if you're actually eligible to sit for the exam on schedule. A few logistical facts worth keeping in view while you plan your study calendar:

• The written examination fee is USD 800; a late application incurs an additional USD 240 fee.
• Eligibility requires AOA board certification in internal medicine, two years of ACGME-accredited or AOA-recognized endocrinology fellowship training, an active medical license, and program-director verification of clinical competence and training completion.
• Fellowship completion is required by August 15 of the examination year.
• The 2026 application window ran February 16-July 16, with the initial subspecialty examination window falling August 12-14.

For the full cost picture, including how the base fee and late fee interact with total preparation spending, see Endocrinology Certification Cost 2026: Complete Pricing Breakdown. If you're unsure whether you currently qualify to sit, our Endocrinology Requirements 2026: Eligibility, Prerequisites & How to Qualify guide walks through each prerequisite in detail, and Endocrinology Exam Dates 2026: Testing Windows, Deadlines & Scheduling covers the full application-to-test-day timeline.

Once certified, maintaining status requires fulfilling Osteopathic Continuous Certification requirements over a 10-year certification period, including active licensure, CME (60 credits per three-year cycle, with 15 Category 1 and/or Category 1-A credits required for the 2025-2027 cycle), a cognitive assessment, and a practice performance assessment. Endocrinology follows AOBIM's traditional subspecialty OCC examination pathway, with recertification exams offered annually in August via remote proctoring - a separate process from the initial 300-question written exam described throughout this guide.

To sharpen your recall of domain-specific facts once you've built a study plan, our Endocrinology Cheat Sheet 2026: One-Page Review of Must-Know Facts condenses the highest-yield points from all 18 domains into a single reference. You can also practice against realistic domain-weighted question sets on our main practice test platform, which mirrors the outline distribution described above. If you're evaluating whether pursuing this credential fits your career goals, Is the Endocrinology Certification Worth It? Complete ROI Analysis 2026 and Endocrinology Salary Guide 2026: Complete Earnings Analysis offer additional context, and Endocrinology Jobs outlines where certified physicians typically practice.

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