Objective: This article seeks to determine whether medical students can estimate the appropriate score for the Global Assessment of Functioning (GAF) compared with psychiatry residents and staff psychiatrists. The authors hypothesized that medical students' estimations of GAF scores for patients in clinical vignettes would differ from those assessed by the psychiatry residents and staff psychiatrists. Method: The authors designed a cross-sectional confidential survey of medical students, psychiatry residents, and staff psychiatrists. Consenting participants were asked to provide demographic information and then complete the accompanying questionnaire after reading two vignettes. One of the vignettes described a depressed patient and the other a psychotic patient. The subjects were asked to estimate the GAF scores for the patients in both vignettes. Then the subjects were given the GAF scoring guide to review and were asked to re-assess their initial GAF scores for the patients in the vignettes. Results: Medical students assigned much higher GAF scores for the patient in the vignette with less severe symptoms than the psychiatry residents and staff psychiatrists. The GAF scores of all three groups for the patient in the vignette with more severe symptoms were comparable. Conclusions: The ability of medical students to assign proper GAF scores needs to be studied further. Our study suggests that current 1-month rotations in psychiatry, without specific training on assigning GAF scores, may not provide medical students with enough information to assess GAF scores accurately. This might need to be addressed in psychiatry clerkships.