Background: The aims of this study were (1) to determine to what extent body mass index (BMI), waist circumference, fat free mass index (FFMI) and skinfold thickness are feasible measurement options in people with intellectual disabilities (ID) to measure their weight status, and (2) to assess the level of agreement among these methods. Methods: BMI, waist circumference, FFMI derived from the Bioelectrical Impedance Analyser and skinfold thickness were all determined in 76 people with intellectual disabilities. Results: BMI and waist circumference could be measured in all subjects. Skinfold thickness and FFMI failed in, respectively, five and 14 people. In general, intertest reliabilities were low. For underweight people, the agreement was acceptable. Conclusions: BMI and waist circumference were feasible measurement options. Agreements among the methods were low. Implications of these results are discussed.