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USMLE study guide: the official content outline

The official guide to what’s on the USMLE is free: the USMLE Content Outline, with separate specifications for each Step showing how much each area counts. There’s no official USMLE textbook. Popular review books like First Aid are written by other publishers, so use the outline as your checklist and pick books that cover it.

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Updated October 2026 · Written from official sources, listed at the bottom of this page

What Step 1 covers

SystemShare of questions
Reproductive and endocrine12-16%
Respiratory and renal/urinary11-15%
Behavioral health and nervous system/special senses10-14%
Blood, lymphoreticular and immune9-13%
Musculoskeletal, skin and subcutaneous tissue8-12%
Multisystem processes and disorders8-12%
Cardiovascular7-11%
Gastrointestinal6-10%
Communication and interpersonal skills6-9%
Biostatistics, epidemiology and population health4-6%
Human development1-3%

Step 1 tests the basic sciences behind health and disease, sorted by organ system. Here are the official ranges by system.

By discipline, pathology is the biggest at 45-55% of questions, followed by physiology at 30-40%. Questions often count toward more than one discipline.

What Step 2 CK covers

Clinical fieldShare of questions
Medicine55-65%
Pediatrics17-27%
Obstetrics and gynecology10-20%
Psychiatry10-15%
Surgery5-15%

Step 2 CK is about clinical care under supervision: diagnosis, tests, treatment and prevention. The official split by clinical field:

Step 3

Step 3 focuses on managing patients on your own, especially in outpatient settings. Day 1, Foundations of Independent Practice, tests the science and basics of care. Day 2, Advanced Clinical Medicine, tests management over time and includes the case simulations. USMLE publishes a Step 3 outline and sample questions too.

Biostatistics, epidemiology and reading the medical literature make up 11-13% of Step 3 multiple-choice questions, the biggest single area by system. On Step 1, the same area is 4-6%. Cardiovascular is 9-11% of Step 3, and respiratory and nervous system are 8-10% each.

Choosing books

First Aid for the USMLE Step 1 is the best-known review book. It’s published by McGraw Hill with a new edition each year, and there are versions for Step 2 CK and Step 3. Many students use it as a summary alongside a question bank.

Whatever you choose, check it against the official outline, and use the newest edition you can. Medicine changes, and so do the specifications. USMLE says the percentages can change at any time.

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Everything else, in one place

OverviewUSMLEQuestions and passingHow many questions are on the USMLE, and what’s the passing score?ScoringHow USMLE scoring worksBookingHow to sign up for and schedule the USMLECostHow much does the USMLE cost?What to bringWhat to bring to the USMLEOnline examCan you take the USMLE online?Step 1USMLE Step 1: pass/fail, format and lengthStep 2 CKUSMLE Step 2 CK scores, percentiles and formatStep 3USMLE Step 3: applying, the two days, CCS and scoresResults and transcriptsWhen do USMLE results come out?Free 120 and self-assessmentsFree official USMLE practice: sample questions and NBME self-assessmentsInternational graduatesThe USMLE for international medical graduatesIf you failFailed a USMLE Step? How retakes workPractice testFree USMLE practice questionsWhere to learnWhere to study for the USMLEStudy plannerUSMLE study planner
Sources: USMLE and 4 more. Checked October 2026.

Rules and fees can change, so check the official site before your test.