Objective: Mental retardation (MR) is a spectrum of disorders characterized by deficits in intellectual and adaptive functioning which could result from several different etiological factors. Studies have shown that people with MR develop mental illness at rates similar to or higher than general population. We have not found any previous study carried out on adults with MR in Turkey. The aim of this study to determine the prevalence of mental disorders in Turkish population and to investigate associated factors. Methods: Participants aged 18 years and above and with a confirmed diagnosis of were recruited from care homes, rehabilitation centers and from people attending to outpatients for the first time for psychiatric assessment. A structured purpose designed Sociodemographic Form was used. Each participant underwent face to face assessment by a psychiatrist and their previous reports were also seen where available. Collateral history was provided by their families or caregivers who had known the person for at least 6 months. Diagnoses were established according to the DSM-5 criteria. Point prevalence of disorders were calculated and associated factors were investigated. Results: 63.5% of the participants met the criteria for one psychiatric disorder, whilst 21% received more than one diagnoses. The most common disorders were as follows: challenging behavior (34%), autism spectrum disorders (13.9%), anxiety-related disorders (13.9%) and attention deficit hyperactivity disorder (10.6%). Living in a care home and being young seemed to be associated with ill mental health. Conclusion: Our study demonstrates high psychiatric comorbidity in adults with MR. Young age and being in a care home seemed to be the only risk factors in our sample. These results highlight a need for increased awareness of mental health professionals and service providers about mental health of adults with MR for early diagnosis and interventions.