Preparing for the USMLE Step 1 requires consistent exposure to high-quality, exam-style practice questions with clear explanations.
On this page, you’ll find 30 free USMLE Step 1 practice questions with detailed explanations, written to match NBME-style logic and commonly tested concepts.
These high-yield MCQs cover pathology, physiology, pharmacology, microbiology, biochemistry, immunology, and anatomy, making this an ideal free USMLE Step 1 question bank for daily practice.
Whether you’re in dedicated study or early preparation, these questions will help reinforce concepts, identify weak areas, and improve test-day confidence.
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30 Free USMLE Step 1 Practice Questions (With Explanations)
1. A patient with hypercalcemia has elevated PTH levels. What is the most likely diagnosis?
A) Secondary hyperparathyroidism
B) Primary hyperparathyroidism
C) Vitamin D deficiency
D) Hypoparathyroidism
Answer: B) Primary hyperparathyroidism
Explanation: Elevated calcium + elevated PTH indicates primary hyperparathyroidism, most commonly due to a parathyroid adenoma.
2. Which enzyme is deficient in classic galactosemia?
A) Galactokinase
B) Aldolase B
C) GALT
D) Hexokinase
Answer: C) GALT
Explanation: Galactose-1-phosphate uridyltransferase deficiency causes vomiting, jaundice, and cataracts in infants.
3. A diabetic patient develops microalbuminuria. The earliest histologic change is:
A) Mesangial expansion
B) GBM thickening
C) Nodular sclerosis
D) Arteriolar hyalinosis
Answer: B) GBM thickening
Explanation: Glomerular basement membrane thickening is an early finding in diabetic nephropathy.
4. Which drug inhibits dihydrofolate reductase in bacteria?
A) Sulfamethoxazole
B) Trimethoprim
C) Penicillin
D) Rifampin
Answer: B) Trimethoprim
5. A patient has ST elevations in leads II, III, and aVF. Which artery is most likely occluded?
A) LAD
B) RCA
C) Circumflex
D) Left main
Answer: B) RCA
Explanation: Inferior wall MI (II, III, aVF) typically involves the right coronary artery.
6. The most common cause of nephrotic syndrome in children:
A) FSGS
B) Membranous nephropathy
C) Minimal change disease
D) IgA nephropathy
Answer: C) Minimal change disease
7. Which cytokine is responsible for fever?
A) IL-1
B) IL-4
C) IL-10
D) IFN-alpha
Answer: A) IL-1
8. A smoker with hematuria most likely has:
A) Renal cell carcinoma
B) Bladder cancer
C) UTI
D) Prostatitis
Answer: B) Bladder cancer
9. The mechanism of ACE inhibitors:
A) Increase angiotensin II
B) Block renin
C) Decrease angiotensin II
D) Increase aldosterone
Answer: C) Decrease angiotensin II
10. Which immunoglobulin crosses the placenta?
A) IgA
B) IgM
C) IgE
D) IgG
Answer: D) IgG
11. A patient with COPD has elevated hematocrit due to:
A) Decreased EPO
B) Increased EPO
C) Hemolysis
D) Iron overload
Answer: B) Increased EPO
12. The most common cause of Cushing syndrome:
A) Adrenal tumor
B) Pituitary adenoma
C) Ectopic ACTH
D) Steroid use
Answer: D) Steroid use
13. Which virus is associated with Kaposi sarcoma?
A) EBV
B) HPV
C) HHV-8
D) CMV
Answer: C) HHV-8
14. Warfarin inhibits:
A) Factor Xa directly
B) Vitamin K epoxide reductase
C) Thrombin
D) Platelets
Answer: B)
15. The most common cause of acute pancreatitis:
A) Alcohol
B) Gallstones
C) Hyperlipidemia
D) Trauma
Answer: B) Gallstones
16. A child with honey-colored crusted lesions likely has:
A) Cellulitis
B) Impetigo
C) Psoriasis
D) Eczema
Answer: B) Impetigo
17. The primary neurotransmitter of the parasympathetic system:
A) Norepinephrine
B) Dopamine
C) Acetylcholine
D) Serotonin
Answer: C)
18. A mutation in p53 leads to:
A) Increased apoptosis
B) Tumor suppression
C) Uncontrolled cell growth
D) DNA repair
Answer: C)
19. Which electrolyte abnormality causes peaked T waves?
A) Hypokalemia
B) Hyperkalemia
C) Hypocalcemia
D) Hyponatremia
Answer: B)
20. The antidote for acetaminophen toxicity:
A) Atropine
B) Naloxone
C) N-acetylcysteine
D) Flumazenil
Answer: C)
21. The most common primary brain tumor in adults:
A) Meningioma
B) Glioblastoma
C) Astrocytoma
D) Oligodendroglioma
Answer: B) Glioblastoma
22. Which enzyme converts pyruvate to acetyl-CoA?
A) Pyruvate kinase
B) Pyruvate dehydrogenase
C) Citrate synthase
D) Lactate dehydrogenase
Answer: B)
23. Graves disease antibodies target:
A) TPO
B) TSH receptor
C) Thyroglobulin
D) Calcitonin
Answer: B)
24. The most common cause of bacterial meningitis in young adults:
A) Listeria
B) E. coli
C) Neisseria meningitidis
D) S. pneumoniae
Answer: C)
25. Heparin works by activating:
A) Protein C
B) Protein S
C) Antithrombin III
D) Plasmin
Answer: C)
26. The most common cause of hyperthyroidism:
A) Toxic multinodular goiter
B) Thyroiditis
C) Graves disease
D) Adenoma
Answer: C)
27. A lesion in the optic chiasm causes:
A) Monocular blindness
B) Bitemporal hemianopia
C) Homonymous hemianopia
D) Scotoma
Answer: B)
28. Beta-blockers decrease:
A) Heart rate
B) Afterload
C) Preload
D) Oxygen saturation
Answer: A)
29. The most common type of shock:
A) Cardiogenic
B) Septic
C) Hypovolemic
D) Obstructive
Answer: C)
30. Lactase deficiency leads to:
A) Protein malabsorption
B) Fat malabsorption
C) Osmotic diarrhea
D) Secretory diarrhea
Answer: C)
Frequently Asked Questions
Are free USMLE Step 1 practice questions enough to pass?
Free questions are excellent for revision and concept reinforcement, but should be combined with full-length practice exams and review resources.
How many practice questions should I complete daily?
Most successful students complete 40–80 questions daily during dedicated study.
Are explanations important?
Yes. The explanation is where learning happens. Focus on understanding why the correct answer is right and why others are wrong.
Is Step 1 still important after becoming pass/fail?
Yes. Strong Step 1 knowledge builds the foundation for Step 2 CK and clinical rotations.