The prevalence of psychiatric morbidity in people with Down syndrome w
as investigated. A prospective study of two-hundred and fifteen indivi
duals using strict methodological criteria-and DCR-10 diagnostic crite
ria was undertaken. The overall frequency of psychiatric disorders was
28.9%. The commonest disorders diagnosed were dementia, depression, c
onduct disorder and obsessive-compulsive disorder. Neurotic disorders
were under-diagnosed with absence of schizophrenia, substance abuse an
d alcoholism.