This study examines the prevalence of overweight and obesity and a panel of potential determinants among French youths and adults with an intellectual disability (ID). The sample used consisted of 1120 youths and adults with an ID, from 5 to 28 years old, attending a French special education school. The results indicated that 19.8% of the participants with an ID are classified as overweight and 8.6% as obese. Multivariate logistic regression analyses revealed that there are nearly three times more girls/women classified as overweight than boys/men. Additionally, they showed that there are nearly two times more participants from southern France classified as overweight than from northern France, and that the risk of being classified as overweight significantly increases with seniority in the school. Next, the interaction effects observed indicated first that there are nearly two times more boys/men on psychotropic medication classified as overweight than boys/men not on psychotropic medication. Second, they revealed that the odds of being classified as overweight for boys/men not on psychotropic medication are 47% lower than for girls/women not on psychotropic medication. Third, they indicated that there are nearly two times more boys/men from southern France classified as obese than boys/men from northern France. Fourth, they showed that the odds of being classified as obese for boys/men from northern France are 52% lower than for girls/women from northern France. In conclusion, these results should be viewed as preliminary and need to be replicated since, to our knowledge, this study is the first one to examine this topic while simultaneously controlling for all of the potential determinants and relying on a sample of youths and adults. (Contains 3 tables.)