Sleepiness is a major public health problem associated with motor vehicle crashes, occupational accidents, decreased productivity, and interpersonal problems. It can be influenced by many factors, including the individual's circadian rhythm. The objective of this study is to assess the correlation between the morningness/eveningness dimension and daytime sleepiness in medical school students. This is a cross-sectional study; 310 subjects (123 women and 187 men, M age 20.5 ± 1.9 yr.) completed a questionnaire on use of drugs, diagnostic diseases, sleeping habits, the Morningness/Eveningness Questionnaire and the Epworth Sleepiness Scale. The only variable related to daytime sleepiness was the morningness/eveningness dimension ( r = –.18, p = .002). Questions with higher coefficients of discrimination between the morning and the evening chronotype were “Lying down to rest in the afternoon when circumstances permit” (.61), “Sitting and reading” (.53), and “As a passenger in a car for an hour without a break” (.53). The implications of the findings are discussed.