OBJECTIVE: Sound clinical judgment is the cornerstone of medical practice and begins early during medical education. The authors consider the effect of personality characteristics (hostility, anger, cynicism) on clinical judgment and whether a brief intervention can affect this process. METHODS: Two sophomore medical classes (experimental, comparison) were assessed on several personality dimensions and responded to a series of clinical vignettes. The experimental group received cognitive behavior training to improve stress, coping, and interpersonal skills. Participants were reassessed within 1 week of the initial assessment. RESULTS: Significant associations between hostility and cynicism and maladaptive responses to the clinical vignettes were noted. Following the intervention, hostility, cynicism, anger, and aggression were significantly reduced, with concomitant reductions in maladaptive decision-making. CONCLUSION: The relationship between the quality of clinical decision-making and personality characteristics was confirmed. The potential to modify this relationship using a brief cognitive behavior intervention suggests that such interventions should be an essential component of medical education.