The association between asthma and sleep disturbances was assessed as part of a community survey of sleep patterns in children aged 4-48 months. A questionnaire covering the area of past and present sleep and settling behaviour, as well as health history and demographic data, was administered to 752 mothers of children visiting 14 well baby clinics. Fifty one (6.8%) of the children who were diagnosed as having asthma by their paediatricians were compared with the remaining healthy controls (children with perinatal problems, other chronic illnesses, developmental problems, or repeat admissions to hospital were excluded). Thirty nine per cent of the children with asthma and 38% of the normal controls were identified as regular wakers. The number of interrupted nights each week, settling time, and sleep duration were comparable. In the children with asthma an uninterrupted night's sleep was acquired later than in the control group. Parental perception of the severity of the sleep problem was similar in the two groups, as were the calming techniques. It is concluded that this study does not support a significantly increased prevalence of sleep disturbances among young children with asthma compared with their healthy peers.