Support for an association between sleep duration and body mass index exists. However, not all short sleepers are overweight/obese. The complex interplay between circadian and metabolic processes has become a recent focus in sleep and obesity research and may explain this perplexing observation. Chronotype (as a marker for circadian misalignment) may be able to predict who is at greatest risk for obesity onset when exposed to short sleep duration. The goal of this study was to examine sleep duration and chronotype in racially/ethnically diverse adolescents and to determine whether chronotype modified the association between sleep duration and body mass index. A cross-sectional study design was used to examine these relationships using self-reported sleep data from 115 9th and 10th grade students and actigraphy-estimated sleep data from 69 of these participants. Participants were recruited from a Northeast coastal city high school in NJ. Socio-demographic and behavioral predictors of sleep duration and chronotype were estimated using general linear models. School night and free night sleep duration, chronotype preference, chronotype, and social jet lag were the independent variables of interest for predicting BMI. The moderating effect of chronotype and social jet lag on sleep duration and BMI was also estimated. General linear models were used to estimate these associations while controlling for selected socio-demographic and behavioral characteristics. Black adolescents had shorter free night sleep than Hispanic adolescents. Adolescents with later chronotypes drank more soda, were less physically active, and napped more frequently than adolescents with earlier chronotypes. Longer school night sleep and greater social jet lag predicted higher BMI z scores. Associations between social jet lag and BMI, as well as chronotype and health-related behaviors, suggest that chronobiological approaches to preventing obesity may be warranted. The overall goal of these approaches should be to align daily schedules with individual biological rhythms. Additional approaches to improve the regularity of sleep-wake timing may be needed. Shorter free night sleep duration in Black adolescents indicate that this group may be at greatest risk for the negative consequences of short sleep and irregular sleep-wake timing.