A cohort of children with Down's syndrome, and their families, have been seen at intervals from six weeks old. Some follow-up data to 21 yrs are reported here. Until 21 yrs when one mother withdrew her son there have been no losses to the study apart from those caused by death. Mean IQs rose slightly from 11 to 21; scores on language and academic tests favoured the home-reared, females, and middle-class young people even when IQ was allowed for. Some of the effects on the family of having a handicapped member were explored; although adverse effects are fewer than might have been expected many parents, especially mothers, carry significant burdens.