Previous work with elderly adults with maturity-onset non-insulin-dependent diabetes has demonstrated the presence of significant learning and memory deficits which are correlated with the degree of chronic hyperglycemia. This study was conducted to examine learning and memory processes in a group of 82 younger adults (mean age = 33.4 years) with a long history (mean duration = 26.2 years) of childhood-onset insulin-dependent diabetes. Contrary to expectation, diabetic subjects performed as well as a group of 82 age- and SES-matched nondiabetic control subjects on all measures of learning and memory. On the other hand, they performed significantly worse on measures of psychomotor efficiency, with degree of chronic hyperglycemia being the best predictor of psychomotor slowing. These findings, together with earlier studies of elderly diabetic patients, suggest that specific neural systems within the aging brain may be differentially sensitive to the "toxic" effects of chronic hyperglycemia.