Overweight and obesity are risk factors for various chronic diseases. Sleep has been associated with overweight and obesity. One potential mechanism by which sleep may lead to overweight and obesity is through positive energy balance (i.e. energy intake exceeding expenditure). There are few studies examining the impact of sleep timing (onset and wake time) on diet and exercise. In a cross sectional study, we examined associations between sleep timing and diet quality, and in separate models, between sleep timing and meeting the 2008 Physical Activity Guidelines for Americans among the participants of the UMass Vitamin D Status Study. A total of 140 young women (aged 18 to 30 years) were grouped into four sleep timing categories based on the median of participants’ sleep onset and wake time (Early sleep-Early wake, Early sleep-Late wake, Late sleep-Early wake, Late sleep-Late wake). Multivariable linear regression and multivariable logistic regression were used to model the associations between the sleep timing categories and diet quality, and sleep timing and meeting the National Physical Activity Guidelines, respectively. Participants in the Early sleep-Early wake group had the highest diet quality scores and were more likely to meet the National Physical Activity Guidelines compared to the other sleep timing categories. To our knowledge, this was the first study in the U.S. examining sleep timing and diet quality and physical activity among young women. In conclusion, the old adage early to bed, early to rise appears to be related to higher diet quality and meeting physical activity guidelines.