© 2019 Elsevier Inc. All rights reserved. Obesity and type 2 diabetes mellitus was previously limited to adults, but in recent decades, there has been an increased prevalence among children and adolescents. Given the cost burden and a plethora of adverse consequences with which these diseases are associated, obesity and cardiometabolic diseases now pose a major public health challenge. Obesity and type 2 diabetes mellitus are chronic conditions that commonly track into adulthood and also increase the likelihood of cardiovascular consequences. While these diseases can be caused by genetics, they are largely driven by lifestyle behaviors. Attempts at addressing the global epidemic have targeted behavior modification such as increasing physical activity levels and controlling dietary intake in the hope of restoring energy balance. Sleep impinges on both side of the energy balance equation and there is now an abundance of evidence to suggest that multiple features of sleep may be contributing to the onset and progression of these chronic conditions, which are discussed in this chapter. In particular, we discuss the literature pertaining to the relationship between sleep and obesity as well as type 2 diabetes mellitus in children and adolescents, while also drawing upon crucial information from adult studies. We also highlight potential mechanisms and make recommendations for future approaches which may enhance the effectiveness of interventions targeting the global epidemic of childhood obesity, which is the main driver of metabolic and cardiovascular diseases.