Purpose: This study represents the first reporting of aggregate data of a longitudinal study designed to identify correlations between medical student personality traits and type of residency, later selected. It is a multisite project involving four US medical schools over a period of nearly ten years. The current study sought to test the hypothesis that relevant personality differences do exist between male and female medical students and discuss the implications of any such findings. Method: Two thousand one hundred and forty four first-year medical students (1008 females and 1136 males) at four medical schools completed the 16PF between 1995 and 2003. Results: A multivariate analysis of variance (MANOVA) was performed to determine if significant gender differences existed for medical students on personality traits, as measured by the 16PF. Results of the MANOVA revealed significant differences (p< .05) for 12 of 16 factors. Conclusions: Results of this study revealed that distinct personality differences existed between male and female medical students. Results suggest that female medical students are more warm and outgoing (Warmth); more dutiful (Rule-Consciousness); more sensitive (Sensitivity); more self-doubting and worried (Apprehension); more organized and self-disciplined (Perfectionism); and more tense and driven (Tension) than their male counterparts. On the other hand, male medical students appear to be more adaptive and mature (Emotional Stability); more forceful and assertive (Dominance); more suspicious and skeptical (Vigilance); more imaginative and idea-oriented (Abstractedness); more private and discreet (Privateness); and more solitary and individualistic (Self-Reliance) as compared to female medical students. It is possible that revealed personality differences between male and female medical students may play a role in later choice of specialty. As such, future analyses of our data set will seek to determine the relationship between such gender differences and later choice of specialty. (Contains 1 table.)