The increase in obesity, including childhood obesity, has developed over the same time period as the progressive decrease in self-reported sleep duration. Since epidemiological studies showed an inverse relationship between short or disturbed sleep and obesity, the question arose, how sleep duration and sleep quality are associated with the development of obesity. In this review, the current literature on these topics has been evaluated. During puberty, changes in body mass index (BMI) are inversely correlated to changes in sleep duration. During adulthood, this relationship remains and at the same time unfavorable metabolic and neuro-endocrinological changes develop, that promote a positive energy balance, coinciding with sleep disturbance. Furthermore, during excessive weight loss BMI and fat mass decrease, in parallel, and related with an increase in sleep duration. In order to shed light on the association between sleep duration, sleep quality and obesity, until now it only has been shown that diet-induced body-weight loss and successive body-weight maintenance contribute to sleep improvement. It remains to be demonstrated whether body-weight management and body composition improve during an intervention concomitantly with spontaneous sleep improvement compared with the same intervention without spontaneous sleep improvement.