Although physicians have been disciplined for a variety of offenses by state medical boards across the United States, limited information is available about the characteristics of these physicians. To assess the characteristics of, offenses committed by, and resulting disciplinary actions taken against a consecutive series of disciplined physicians in the state of Ohio, the authors conducted a case-control study of all 308 physicians publicly disciplined by the State Medical Board of Ohio (SMBO) from January 1997 to June 1999. Subjects were matched with two groups of control physicians--one matched by location only, and the second matched for location, gender, practice type, and self-designated specialty. The main outcomes measured were disciplinary actions, offenses leading to state medical board actions, and the characteristics of disciplined physicians. Of 340 physicians disciplined during these 30 months (approximately 0.37% per year), 308 committed 477 offenses requiring 409 actions by the SMBO. The most common offenses were impairment due to alcohol and/or drug use (21%), inappropriate prescribing or drug possession (14%), previous state actions (15%), negligence or incompetence (7%), and drug-related charges (7%). Although offenders were significantly less likely to be women (P < .05; odds ratio [OR], 0.46; 95% confidence interval [CI], 0.28-0.75), the authors found no difference in the severity of disciplinary action taken against offenders by gender (OR, 1.23; 95% CI, 0.54-2.82) or by type of medical training, ie, between osteopathic physicians and allopathic physicians (OR, 0.70; 95% CI, 0.39-1.26). Compared with controls matched for location, gender, practice type, and self-designated specialty, offenders were significantly less likely to be board certified (OR, 0.65; CI, 0.46-0.92) and significantly more likely to have been in practice 20 or fewer years (OR, 1.51; 95% CI, 1.08-2.13). Disciplinary actions in Ohio were more frequent, more severe, and more often in response to impairment due to alcohol and/or drug use and previous state actions than previously reported. No difference in the severity of disciplinary action was noted between men and women or between osteopathic and allopathic physicians.