Prevalence of intellectual disability in northern Sydney adults

The prevalence of intellectual disability, defined as IQ < 70, was determined in a population of adults aged 20-50 years who lived in the northern suburbs of Sydney, Australia. Case finding was carried out in the community, and all those ascertained were interviewed and psychometrically assessed. The overall prevalence was 3.31 per thousand with severe intellectual disability (IQ < 55) 2.19 per thousand and mild (IQ 56-70) 1.12 per thousand. Down's syndrome had a frequency of 0.96 per thousand. Thirty-eight per cent of the total group were living in institutional care.