Little research has been conducted to examine diet quality of overweight and obese adults with intellectual and developmental disabilities (IDD) in the United States. The purpose of this study was to determine diet quality, as measured by the Healthy Eating Index-2005 (HEI-2005), of overweight and obese adults with IDD. Data were obtained from community-dwelling overweight individuals. 3-day food records were administered and completed with assistance by staff or family members and then reviewed by a dietitian. All records were analyzed and HEI-2005 was calculated using NDSR output. 178 records were analyzed from 70 subjects (28 male, 42 female; mean age 33.9 ± 11.5 years). The mean energy intake was 1928 ± 891 kcals, and the mean total HEI-2005 score was 46.7 ± 11.5. Participants scored the lowest in total fruits, whole grains, dark green and orange vegetables, non-hydrogenated vegetable oils, and sodium. Both male and female participants had diets deficient in fiber, vitamin A, vitamin D, vitamin E, folate, and potassium. Additionally men were deficient in vitamin K, and women were deficient in calcium. Overweight and obese adults with IDD had a lower HEI-2005 score compared to the general population and are at an increased risk of poor diet quality and nutritional deficiencies that could contribute to the development of diabetes, cardiovascular disease, cancer and other health complications.