BackgroundPoor diet may contribute to the high rates of overweight and obesity (OW/OB) in adolescents and young adults with intellectual disabilities (ID). ObjectiveThe purpose of this study was to examine diet quality as assessed by Healthy Eating Index 2015 (HEI-2015) scores in adolescents and young adults with ID and OW/OB, and to compare diet quality by ID diagnosis and weight. DesignThree-day image assisted food records from baseline assessments in an 18-month weight loss trial for adolescents and young adults with ID and OW/OB were used to calculate HEI-2015 scores which were compared between ID diagnoses and weight categories. Participants/settingA total of 102 adolescents and young adults (13-21 y/o) with ID (48 with Down syndrome; 40 with autism; 14 with other/unspecified ID) and OW/OB at a Midwestern academic medical center completed valid food records from November 2015- November 2019. Main Outcome MeasuresOutcome measures included HEI-2015 scores, energy intake (kcal/day), macronutrient intake as percentage of energy, energy intake/kg body weight, and grams protein/kg body weight. Statistical analyses performedDifferences in HEI-2015 scores and additional dietary measures by weight category and ID diagnosis were examined with ANOVA or Kruskall-Wallis tests. ResultsParticipants with Down syndrome (DS) had a significantly higher mean ± SD HEI-2015 score (53.9±8.4) compared to participants with autism (49.1±9.6), p=0.047. Compared to those with autism, participants with DS had higher percentage of energy from protein, higher energy intake/kg body weight, and higher grams protein intake/kg body weight. For HEI-2015 components, participants with DS had higher scores than participants with autism for total fruits, whole fruits, total vegetables, greens & beans, and total protein foods, but lower scores for sodium. Diet quality was not observed to differ by weight classification. ConclusionsAdolescents and young adults with autism had lower overall diet quality scores compared to those with DS. Diet quality was not found to be related to OW/OB. Understanding dietary differences by ID diagnosis may inform intervention strategies.