Data on psychiatric problems in adults with autism are inconsistent, with estimated rates ranging from around 25% to over 75%. We assessed difficulties related to mental health in 58 adults with autism (10 females, 48 males; mean age 44?years) whom we have followed over four decades. All were of average non-verbal intelligence quotient when diagnosed as children. Overall ratings of mental health problems were based on data from the Family History Schedule (Bolton et al., 1994). Informant reports indicated that many of the cohort (44%) had experienced no mental health problems in adulthood; 28% had experienced mild to moderate difficulties, 23% had severe and 5% very severe problems. Depression was the most commonly reported problem. Among those adults (n?=?22) able to report on their own mental state, again many (45%) reported no mental health problems, although 27% reported very severe mental health problems related to anxiety, depression and/or obsessive-compulsive symptoms. Informant ratings of poor mental health were not associated with gender, severity of autism in childhood, or child or adult intelligence quotient, but there were small correlations with overall social functioning (rho?=?0.34) and current autism severity (rho?=?0.37). The findings highlight the difficulties of assessing mental health problems in adults with autism and the need for appropriately validated measures.