SummaryObesity is a well-known risk factor for the development of non-insulin-dependent diabetes mellitus (NIDDM). Both insulin resistance and concomitant B-cell dysfunction are necessary for the development of NIDDM. Insulin resistance, probably genetically determined but worsened by obesity, appears to be the primary defect that leads to impaired glucose tolerance. However, B-cell dysfunction plays a critical role during progressive deterioration from mild impaired glucose tolerance to severe NIDDM.