ABSTRACT.This paper is in two parts. The first part reviews the available literature describing sleep patterns of people with mental handicap and the nature and prevalence of sleep disorders amongst this client group. Both electroencephalographic studies and informant‐based reports are included. The literature is small, particularly in terms of the latter reports, and most of the information from both E.E.G. and informant sources describes populations of children with mental handicap. The need for further investigation of sleep and sleep problems, particularly amongst adults with mental handicap, therefore, becomes evident. The second part presents the results of a detailed sleep survey of 120 adults with mental handicap, approximately half of whom were resident in hospital and half in the community. A descriptive summary of the total sample is provided. Fifteen per cent of the sample presented significant sleep problems, particularly in the form of intermittent wakenings. The results of comparisons between (1) good and poor sleepers (2) hospital and community residents and (3) people with mental handicap and‘normal’adults (using data from another study) are then presented. The relationships between sleep and daytime functioning and the potential usefulness of behavioural approaches to management of sleep pattern are disc