Prevalence of psychiatric illness in people with learning disabilities (LD) may be slightly higher than that in the normal population, especially when the difficulties of diagnosis in the learning disabled population is taken into account. Cooper & Collacott, in a review article, suggested that rates of affective disorder among people with a learning disability may be as low as 1–5%. Corbett, in his Camberwell study of people with LD, aged 15 years and older, found rates of present or past significant affective disorders of 5.5%. A population-based study of adults with Down syndrome reported rates of depression of 11%. Psychiatrists working with people with PWS have come to speculate that rates in PWS may be higher than those in the general LD population, and that general depression and anxiety may not be the most common symptoms found in PWS. A study that looked at psychiatric symptoms in 23 people with PWS (genetically confirmed in 20 cases) and a comparison group of 73 people with other LD found higher rates of affective disorder (4/23 v. 3/73), schizophrenia/delusional disorder (1/23 v. 2/73), and obsessive—compulsive disorder (OCD) (1/23 v. 2/73) in PWS compared with other causes for LD. Unlike the LD group, there were no cases of generalised anxiety disorder, agoraphobia, other phobias, alcoholism, dementia or autism in the PWS group. In a group of 35 adolescents with PWS, it was estimated that more than half had definite or probable DSM-III diagnoses, compared with 18.7% of the general population.