There is renewed interest in the relationship between birth weight and type 2 diabetes. Previous case-control studies (1) of elderly European residents showed a linear association between low birth weight and type 2 diabetes. More recent cohort studies (2) in Pima Indians have shown a U-shaped curve between birth weight and diabetes, where both low and high birth weight were shown to increase the risk for developing type 2 diabetes. In addition, a few studies (3,4) found an association between high birth weight and type 2 diabetes in Caucasian populations. Using the resources of the Rochester Epidemiology Project (REP), we examined the association of birth weight and type 2 diabetes in individuals who were born and developed type 2 diabetes while residing in Rochester, Minnesota. The unique resources of the REP were used to construct the Rochester Diabetes Incident cohort. As described elsewhere (5,6), case assignment was determined by retrospective review of each patient’s complete (hospital and ambulatory) medical records by trained nurse abstractors under the direction of an endocrinologist (P.J.P.). The records were reviewed for all laboratory glucose values and for evidence of any antidiabetic medication over the entire duration of residence in the community. Standardized case criteria were applied that approximated the National Diabetes Data Group recommendations, and adjustments were made for temporal changes in laboratory methods (7 …