Objectives: To determine attention performance of medical students after sleep deprivation due to night shift work.Methods: Prospective cohort design.All seventh, eighth and ninth semester students were invited to participate (n= 209).The effectiveness and concentration indices (d2 Test for attention, dependent variable) from 180 students at 3 evaluations during the semester were compared.Eighth and ninth semester students underwent their second evaluation after a night shift.The independent variables were nocturnal sleep measurements.Results: No differences in nocturnal sleep hours during the previous week (p=0.966),sleep deprivation (p=0.703) or effectiveness in the d2 Test (p=0.428) were found between the groups at the beginning of the semester.At the beginning and the end of the semester, the d2 Test results were not different between groups (p=0.410,p=0.394) respective-ly.The second evaluation showed greater sleep deprivation in students with night shift work (p<0.001).The sleep deprived students had lower concentration indices (p<0.001).The differences were associated with the magnitude of sleep deprivation (p=0.008).Multivariate regression analysis showed that attention performance was explained by sleep deprivation due to night shift work, adjusting for age and gender.Students with sleep deprivation had worse concentration than those without.Conclusions: Sleep deprivation due to night shift work in medical students had a negative impact on their attention performance.Medical educators should address these potential negative learning and patient care consequences of sleep deprivation in medical students due to night shifts.