Emerging data indicate that the timing and rhythms of energetic behaviors may influence metabolism and obesity risk. Our aim was to derive diurnal rest-activity patterns from actigraphy in adolescents and analyze associations with adiposity measures and cardiometabolic risk factors. Adolescents in the Project Viva cohort wore a wrist actigraph over 7 days. We derived markers of daily rest-activity patterns from actigraphy using nonparametric models, generating measurements of relative amplitude (RA). RA reflects the normalized difference in activity measured during the most active 10-hour period and the least active 5-hour period, averaged over multiple 24-hour periods. Using multivariable-adjusted linear regression models, we estimated associations of RA and its components with markers of adiposity (body mass index, waist circumference, skinfolds, dual-energy X-ray absorptiometry fat mass) and cardiometabolic health (cardiometabolic risk score, derived as the mean of five sex-specific internal z-scores for waist circumference, systolic blood pressure, high-density lipoprotein cholesterol scaled inversely, and log-transformed triglycerides and homeostatic model assessment of insulin resistance). A total of 778 adolescents provided at least 5 days of valid actigraphy data. The average age was 13.2 (±.9) years, 52% were female, and the average RA was .9 (±.1). A higher RA reflecting higher activity during wakefulness and lower activity during the night was associated with more favorable indices of adiposity (e.g., -.35 kg/m2 lower body mass index per each .04 units increment of RA; 95% confidence interval: -.60 to -.09). In this large sample of adolescents, a higher RA emerged as a novel biomarker, associated with more favorable cardiometabolic profiles.