Abnormalities in the lipid composition of erythrocytes can alter blood rheology and viscosity. These alterations have been implicated in the pathogenesis of microvascular disease in diabetic patients. The present study was undertaken to examine whether or not long-term glycemic control or duration of diabetes has any role in the altered membrane cholesterol and phospholipid composition of erythrocytes in type I diabetes. Long-term glycemic control was assessed by measuring glycosylated hemoglobin (GHb) from diabetic patients and age-matched normal volunteers. There was no significant correlation between GHb or duration of diabetes with total cholesterol, phospholipid, and cholesterol to phospholipid molar ratios in erythrocytes of these patients. Among phospholipid classes, GHb showed a significantly negative relationship with sphingomyelin (SM) ( r = .55, P < .01) levels, but was not related to phosphatdylcholine (PC) and phosphatidylethanolamine (PE) levels of erythrocytes. Duration of diabetes had no effect on SM, PC, or PE levels of erythrocytes.