Fasting during Ramadan is distinct from regular voluntary or experimental fasting. This project was conducted to objectively assess the effect of Ramadan fasting on sleep architecture, daytime sleepiness and the circadian cycle of melatonin level. Eight healthy volunteers reported to the Sleep Disorders Center on four occasions for polysomnography and multiple sleep latency tests: 1) an initial visit for adaptation; 2) 2 weeks before Ramadan (BL); and 3,4) during the first and third weeks of Ramadan (R1, R3). Salivary melatonin level was measured using radioimmunoassay. Sleep latency at night was significantly shorter and the amount of rapid eye movement sleep was significantly less, at R3 compared to BL. There was no difference in multiple sleep latency test data between BL and Ramadan. Although melatonin level kept the same circadian pattern at BL, R1 and R3, it had a flatter slope and a significantly lower peak at midnight (00:00) at R1 and R3. This study showed a significant reduction in sleep latency and rapid eye movement sleep during the third week of Ramadan fasting. Otherwise, there was no significant effect of Ramadan on sleep architecture and assessment revealed no increase in daytime sleepiness. Although melatonin level had the same circadian pattern during Ramadan, the level of the hormone dropped significantly from baseline.