Objective: The goal of this study was to evaluate a recent medical school curriculum change at our institution 3 years ago; specifically: shortening the Psychiatry core clerkship from 4 to 3 weeks and adding an optional 6-week core/elective combination rotation in lieu of the 3-week core. The authors aimed to determine whether clerkship length was associated with lower scores on the NBME Psychiatry shelf exam (PSE), a requirement of all third-year medical students at our institution. Method: Authors collected a convenience sample of 12 years of shelf-exam scores from all Mayo medical students and determined the length of each student's clerkship. Creating three groups (6-week core/elective [N=14], 4-week clerkship [N=478], and 3-week clerkship [N=24]), they determined the mean exam score for each group and compared the means across the three groups by use of one-way ANOVA. Results: The mean shelf-exam score for each group was: 81.5 (6 weeks), 75.3 (4 weeks), and 75.5 (3 weeks), a significant difference between 6 versus 4 weeks and 6 versus 3 weeks, but not 4 versus 3 weeks. Conclusions: Students completing 3 weeks in psychiatry had an average shelf score almost identical to those completing 4 weeks, but both 3- and 4-week clerkship groups had exam scores significantly lower than students who completed 6 weeks of psychiatry clerkship. The authors propose that differences between groups are the result of shorter clerkship lengths, but other factors, including differences between student cohorts or differences between individual students, may also be involved.