As the last examination in the United States Medical Licensing Examination (USMLE) sequence, Step 3 provides a safeguard before physicians enter into unsupervised practice. There is, however, little validity research focusing on Step 3 scores beyond examining its associations with other educational and professional assessments thought to cover similar content. This study examines the associations between Step 3 scores and subsequent receipt of disciplinary action taken by state medical boards for problematic behavior in practice. It analyzes Step 3 total, Step 3 computer-based case simulation (CCS), and Step 3 multiple-choice question (MCQ) scores. The final sample included 275,392 board-certified physicians who graduated from MD-granting medical schools and who passed Step 3 between 2000 and 2017. Cross-classified multilevel logistic regression models were used to examine the effects of Step 3 scores on the likelihood of receiving a disciplinary action, controlling for other USMLE scores and accounting for jurisdiction and specialty. Results showed that physicians with higher Step 3 total, CCS, and MCQ scores tended to have lower chances of receiving a disciplinary action, after accounting for other USMLE scores. Specifically, a 1-standard-deviation increase in Step 3 total, CCS, and MCQ score was associated with a 23%, 11%, and 17% decrease in the odds of receiving a disciplinary action, respectively. The effect of Step 2 CK score on the likelihood of receiving a disciplinary action was statistically significant, while the effect of Step 1 score became statistically nonsignificant when other Step scores were included in the analysis. Physicians who perform better on Step 3 are less likely to receive a disciplinary action from a state medical board for problematic behavior in practice. These findings provide some validity evidence for the use of Step 3 scores when making medical licensure decisions in the United States.