Background: Studies of resident fatigue and performance have shown mixed results. However, research has not examined daytime sleepiness and performance among attending physicians. The purpose of this study was to explore the relationship between sleep, performance and prefrontal cortex (PFC) activity. We hypothesized that sleepiness scores would negatively correlate with multiple-choice question (MCQ) performance and would also correlate with PFC activity. Methods: Board-certified physicians completed an Epworth Sleepiness Scale (ESS) and then answered MCQs from licensing examinations while in a functional Magnetic Resonance Imaging (fMRI) scanner. Results: Seventeen board-certified internists completed the study. The mean number of correct responses was 18.5/32. The correlation between the ESS and MCQ score was -0.30, and higher ESS scores were negatively associated with statistically significant changes in medial PFC (mPFC) activity. Conclusions: Attending physicians who reported higher sleepiness scores performed worse on licensing exam questions. Notably, our cohort had normal to mild sleepiness scores. Moreover, higher sleepiness scores were negatively associated with changes in mPFC activity on fMRI, which is consistent with emerging work implicating the PFC in fatigue-related cognitive impairment. Our findings have implications regarding the impact of sleep on physician performance during examinations and potentially on their care of patients.