Background: The purpose of this study was: (1) to evaluate the beliefs, attitudes and behaviours associated with nutrition and physical activity of parents with adolescents with intellectual disabilities (ID); (2) to determine if these variables related to the body mass index (BMI) of the adolescents and the parents' BMI; and (3) to investigate if the parents' perception of their child's weight status was accurate. Methods: A survey was used to collect information on BMI and attitudes and beliefs about nutrition and physical activity from parents (n = 207) of adolescents with ID attending schools participating in the "Best Buddies Program." Results: Approximately 45% of the adolescents were overweight or obese and over two-thirds of the parents were either overweight or obese. There was a significant difference in child's BMI by parents' description, F[subscript 3,158] = 72.75, P less than 0.001. Factor analysis on questions on physical activity and nutrition revealed three factors (Factor 1--Family Healthy Habits, Factor 2--Parental Role and Factor 3--Parental Activity) extracting 63% of the variance. The BMI of the adolescents significantly correlated with Factors 2 and 3. Children categorised as having a lower BMI had parents who agreed significantly more (r = -0.22, P less than 0.005) with questions about being role models. There was a significant correlation between BMI for both the parents and adolescents and frequency of fast foods purchased. Conclusion: Efforts need to be made to provide parents of adolescents with ID tailored information about how they can assist their child in managing their weight. This information should emphasise to parents the important part they play as role models and as providers for healthy choices for physical activity as well as nutrition.