Although many researchers have investigated emotional and behavioral difficulties in individuals with Williams syndrome, few have used standardized diagnostic assessments. We examined mental health problems in 92 adults with Williams syndrome using the Psychiatric Assessment Schedule for Adults with Developmental Disabilities--PAS-ADD (Moss, Goldberg, et al., 1996). Factors potentially associated with mental health problems were also explored. The PAS-ADD identified mental health problems in 24% of the sample. The most common were anxiety (16.5%) and specific phobias (12%). Other diagnoses included depression, agoraphobia, and social phobia. No association was found between the presence of mental health problems and either individual (e.g., age, IQ, language level) or external (life events) variables.