OBJECTIVE To investigate the extent to which Medical College Admission Test (MCAT) subscores predict the overall academic performance of osteopathic medical students. METHODS We examined the value of MCAT subscores in predicting students' global academic performance in osteopathic medical school, as defined by grade point average in basic science (basic GPA), clinical instruction (clinical GPA), cumulative grade point average (total GPA), and national licensing examination scores on the Comprehensive Osteopathic Medical Licensing Examination-USA (COMLEX-USA) Level 1 and Level 2. Subjects were 434 osteopathic medical students of the Oklahoma State University College of Osteopathic Medicine in Tulsa who either graduated or were expected to graduate between the years 1999 and 2003. Standard, multivariate linear regression analyses were conducted for each of the five performance variables to assess the relative importance of MCAT subtest scores and cumulative undergraduate GPA (total UGPA) in predicting academic performance. RESULTS Total UGPA was the most important, significant predictor (beta=.13-.33) in overall student academic performance for all five analyzed variables. Less predictive of overall academic performance (beta=-.01-.21) were MCAT subcores. However, the MCAT biological sciences subscore was a significant predictor of basic GPA (beta=.14), the MCAT physical sciences subscore significantly predicted COMLEX-USA Level 1 scores (beta=.15), and the MCAT verbal reasoning subscore significantly predicted COMLEX-USA Level 2 scores (beta=.21). The subscore for the MCAT writing sample was not a significant predictor of overall academic performance. CONCLUSIONS Total undergraduate GPA had the highest predictive value for academic performance as measured by basic GPA, clinical GPA, total GPA, and COMLEX-USA Level 1 and Level 2 scores. The present study found MCAT subscores to be of limited predictive value in determining global academic performance.