Overweight and obesity are major health problems associated with increased cardiovascular disease risk, which is not sufficiently studied in people with intellectual disability yet. The present study was part of the Healthy Ageing in Intellectual Disability (HA-ID) study. The aim of this study was to establish (1) the prevalence of overweight, obesity and body fat percentage in older people with intellectual disability (ID) through measurement of Body Mass Index (BMI), waist circumference, waist-to-hip ratio (WHR) and skin fold thickness, and compare this with prevalence of overweight and obesity in the general population, and (2) the association of overweight and obesity with participant and treatment characteristics (gender, age, level of ID, Down syndrome, autism, independent living, smoking, (instrumental) activities of daily living ((I)ADL), physical activity and use of atypical antipsychotic medication) using regression analyses. In this cross-sectional study 945 persons, aged 50 and over with borderline to profound ID, living in central settings, in community settings and independently were included. Overweight and obesity were highly prevalent, with more obesity (26%) than in the general Dutch older population (10%) as measured by BMI, and 46-48% obesity as measured by waist circumference and WHR respectively. Women, people with Down syndrome, higher age, less severe ID, autism, people who are able to eat independently, preparing meals and doing groceries independently, people with physical inactivity and use of atypical antipsychotics were significantly more at risk of being overweight or obese. This merits specific actions by policy makers and clinical practice to improve health outcomes. (Contains 4 tables.)