Obesity is believed to be a promoter of type 2 diabetes mellitus (T2DM). Reports indicate that severe obesity in childhood and adolescence increases the risk of T2DM in youth and young adults. T2DM, which is commonly asymptomatic, frequently is not recognized until random blood glucose is measured. Screening blood glucose levels measured in obese individuals are more effective for identifying undiagnosed persons, than screening the general population and therefore introduces a selection bias for discovery. The following commentary will indicate why these observations do not indicate that obesity is the cause of T2DM. Also, it will be shown that the insulin resistance of T2DM occurs primarily in the muscles of lean individuals predisposed to diabetes before they become obese. This insulin resistance is not secondary to, but instead, is the cause of the excessive fat accumulation associated with T2DM. Moreover, this early muscle insulin resistance is the etiology of the hyperlipidemia and excess fat accumulation characteristic of T2DM.