Few epidemiological data have been reported on the relation between Ramadan fasting, life habits (meal frequency, sleep habits) and daytime sleepiness during Ramadan. This paper presents the results of a detailed study of the chronotype and daytime sleepiness before and during Ramadan. It was conducted on a sample of 264 subjects aged between 20 and 30 years. Results have revealed a significant decrease in the meal frequency during Ramadan compared with the control period. Before Ramadan, the majority of subjects woke up between 6 and 7 a.m. and went to sleep between 10 and 11 p.m. however, during Ramadan fasting, they woke up after 8 a.m. and preferred to go to sleep later (after midnight). Chronotype as evaluated by the Horne and Ostberg scale was changed significantly during Ramadan: an increase of the evening type and a decrease in the morning type of subjects was observed. Daytime sleepiness as evaluated by the Epworth Sleepiness Scale was significantly increased.