Abstract Objective To examine whether body mass index (BMI), sleep duration, and daytime sleepiness differed by ADHD diagnostic status, and to investigate the role of sleep duration and daytime sleepiness in the ADHD-BMI relationship. Participants Participants were 72,040 18–25-year-old respondents to the American College Health Association National College Health Assessment III (ACHA-NCHA III). Method Welch’s t-tests and a serial mediation model were conducted.