OBJECTIVE: Sleep changes during Ramadan in nonfasting individuals have not been assessed before. We aimed to assess the effect of the attending lifestyle changes during Ramadan on sleep behavior and chronotype in fasting and nonfasting individuals. METHODS: Participants completed predesigned questionnaires to assess sleep patterns, daytime sleepiness, meal habits, and chronotype one week before Ramadan (BL) and during the first week (R1) and third week (R3) of Ramadan 1424 (Hijra) (between October 26 and November 15, 2003). Participants were divided into to 3 groups: fasting Saudis (SF), fasting non-Saudis (NSF), and non-fasting non-Saudis (NF). The study was conducted in Riyadh, Kingdom of Saudi Arabia. RESULTS: Complete data were available on 41 subjects in the SF group, 30 in the NSF, and 30 in the NF group. There was no changes in total sleep time or daytime sleepiness in all 3 groups. In the fasting groups (SF and NSF), bedtime and wake-up time were delayed significantly at R1 and R3 compared to BL, the frequency of meals decreased significantly during Ramadan, and morningness/eveningness test showed an increase in the evening types during Ramadan. In the NF group, bedtime was delayed significantly during Ramadan, and morningness/eveningness test showed an increase in neither types and reduction in the morning types during Ramadan. CONCLUSIONS: Sleep behavior changes during Ramadan in nonfasting participants indicate that the attendant lifestyle changes during Ramadan have a significant effect on sleep behavior. Factors other than fasting may play an important role in modifying an individual's behavior during Ramadan.