Prevalence rates vary considerably regarding the mental health of people with learning disabilities. This variation is a consequence of the assessment methods used to identify such clinical conditions and also different populations studied. The aim of this study was to screen for mental health problems in adults with mild-to-moderate learning disabilities. This study took place in one region of the UK providing community-based services to 96 adults with mild-to-moderate learning disabilities. Using the Mini PAS-ADD Interview schedule, a number of specifically trained interviewers, interviewed staff who supported these adults with learning disabilities in their particular work/day care setting to determine whether or not participants had a potential mental health problem. This study found a 33.3% prevalence rate of mental health problems in this community sample. This sample was found to score higher on the sub-scales of depression and psychosis compared with other prevalence studies. The Mini PAS-ADD Interview was found have an overall sensitivity of 1 (100%); its specificity was 77%. The results of this study fall between previous community prevalence studies that range from 14% to 50%. The practical issues of the screening process are discussed. Methodological limitations are also highlighted in accurately predicting prevalence rates of mental health problems in the learning disability population by clinical staff.