A study of the dietary intake of 115 male and 217 female mentally handicapped persons aged 15-64 years in five long-stay institutions was carried out using a semi-weighed technique over 4 d. Nineteen per cent of males and 5% of females were classified as being underweight and 15% of males and 27% of females were classified as being obese. The average daily intakes of nutrients were: energy 8.8 MJ, protein 92 g, carbohydrate 218 g, fat 101 g, dietary fibre 18 g, calcium 1024 mg, iron 12.5 mg, vitamin B6 1.4 mg, vitamin B12 10.8 micrograms, ascorbic acid 68 mg. The distribution of energy between protein, carbohydrate and fat was 18, 39 and 43% respectively. Energy intakes were not related to ambulatory status, degree of mental handicap, the level of drug usage or body mass index. Energy intakes varied significantly between hospitals and between the sexes.