The sleep patterns of 174 infants were recorded on one typical day at six, 13, 26 and 52 weeks of age, using a 24-hour log. During the first year of life the number of episodes of sleep was reduced by about 50 per cent, but total sleep time was reduced by only two hours. A circadian rhythm was established by six weeks of age. Smaller infants slept more than larger ones in the first months of life. Sex or birth-order of the child did not affect the duration or number of sleep episodes, but sleep pattern related significantly to whether or not mothers found their infants difficult to feed. Introduction of weaning food at an early stage reduced the number of sleep episodes, but increased the average length of each episode. Socio-economic status showed no significant relationship with number of episodes or total length of sleep.