Background: The aim of this study was to investigate the prevalence of and the factors associated with psychiatric symptoms (PS) and challenging behaviour (CB) in adults with intellectual disabilities, and the utilization of psychiatric services in Turkey. Method: Psychiatric Assessment Schedule for Adults with Developmental Disorders Checklist-Revised was used for PS and a structured form for other variables in 771 participants. Results: Of the participants, 50.1% had PS and 36.4% presented with CB. Multivariate analysis revealed that a higher level of needs, better verbal ability, residential living, incontinence and CB, and lifetime suicidal ideation/attempt were independently associated with PS. For CB, it emerged as male carer, PS, lifetime suicidal attempt/ideation, lower level of verbal ability and autism spectrum disorder. Barriers were experienced by 64.7% of participants within the previous year. Conclusions: Psychiatric symptoms and CB seem to be problems for a significant proportion of adults with intellectual disabilities in Turkey, and there are certain barriers to psychiatric services.