The study will assess the effects of weight loss on sleep disordered breathing in 120 obese, Type 2 diabetics with obstructive sleep apnea (respiratory disturbance index [RDI] greater than or equal to 15) who are randomly assigned to either weight loss (n=60) or usual care (n=60) treatments within the context of the Look AHEAD study. Home polysomnography studies will be performed before treatment and at one and two years. Among the 60 weight loss subjects, the investigators will assess the relative importance of changes in neck and abdominal fat in explaining the variability of changes in sleep disordered breathing after weight loss. Finally, they will examine the relationship between changes in sleep-disordered breathing and changes in blood pressure after weight loss in the 60 weight loss participants. Specifically, this research will: 1) determine the efficacy of a weight loss program in reducing sleep disordered breathing in obese Type 2 diabetics; 2) identify sources of variability in sleep disordered breathing associated with weight loss; and 3) examine the role of sleep disordered breathing in mediating changes in blood pressure associated with weight loss. The results of this study will provide an empirical basis for making recommendations about the effectiveness of weight loss in Type 2 diabetics with OSA.