Background: The PAS-ADD Checklist is designed to screen for likely mental health problems in people with intellectual disabilities (ID). The specificity of recommended subscales derived from diagnostic criteria is unclear. This paper therefore investigates the factor structure of the PAS-ADD Checklist to determine the adequacy of empirically derived subscales. Method: A total of 1,115 informants who had known service users for a median of 24 months completed the PAS-ADD Checklist on 1,155 adults with ID living either in the community, in residential care, or in hospital settings in a county in North-East England. Results: The sample was randomly divided into two, with all item scores dichotomised. An exploratory principal components factor analysis with varimax rotation was conducted on Subsample A, producing an optimal 7-factor solution. However, a confirmatory factor analysis using this factor structure for Subsample B revealed a mediocre to poor fit. Further exploratory and confirmatory factor analyses also indicated that empirically derived PAS-ADD Checklist subscales were inconsistent. Conclusion: Given the inconsistency of empirically derived subscales, we do not recommend using the PAS-ADD Checklist to identify specific types of psychopathology. The Checklist may have more utility as a screening tool for general psychopathology and subsequent referral for more detailed assessment. (Contains 1 table.)