Objectives This study examined the incidence and severity of impostorism in third-year medical students as they transitioned from the preclinical to clinical phases of training. Methods A cross-sectional study was conducted in third-year medical students (N=215). Respondents completed a voluntary, anonymous, 60-item survey that included the Clance Impostor Phenomenon Scale and the Perceived Stress Scale. Student’s-t, Mann-Whitney, and Chi-Square tests and Pearson correlation were used to determine differences between subgroups of students and relationships between instruments scores and demographic parameters. Results Fifty-nine percent of students responded with N=112 (59% female) completing at least one instrument. The mean impostor score was 63.0 ± 14.6 (moderate-to-frequent impostor feelings) and was 9% higher in females (U=1181, p = .046). Perceived Stress scores for females were 17% higher than males (t(109)=2.87, p=.005). Females had lower United States Medical Licensing Examination (USMLE) Step 1 scores (t(107)= 3.06, p=.003). Impostor and perceived stress scores were correlated for males (r(46)=.47, p=.002) and females (r(64)=.54,p<.0001). Impostor and USMLE Step 1 scores were negatively correlated for males (r(45) =-.32, p= .034) but not females (r(63) = -.11, p=.40). Conclusions These findings demonstrate the intercorrelation between impostorism and stress in male and female medical students and raise interesting questions regarding the contributions of gender and other factors involved with medical training.