Hyperglycemia is an important risk factor for the development of retinopathy and nephropathy in people with diabetes mellitus. There are few population-based data on changes in glycemia over time. The purpose of this study was to examine changes in glycemia, as measured by glycosylated hemoglobin in 1980 to 1982 and in 1984 to 1986, in a large population-based study of people who were diagnosed to have diabetes before the age of 30 years and who used insulin (n = 697). Glycosylated hemoglobin was measured by a microcolumn technique at both examinations. There was a significant (P < .001) fall in the mean glycosylated hemoglobin from 10.8 to 10.1% over the 4-year interval of the study. In contrast, there was no change in the glycosylated hemoglobin (6.2%) in a similarly aged nondiabetic comparison group over the same period. The decrease in mean glycosylated hemoglobin over the 4-year period in the diabetic group was associated with several characteristics of diabetes management. These include changes in the insulin regimen (going from intermediate- or long-acting insulin only to combinations with short-acting insulin), an increase in the number of doses of insulin per day, and a higher frequency of self-monitoring of blood glucose level. It was also associated with an increased number of reported insulin reactions. These data suggest that recent changes in treatment and management of diabetes may be related to a significant decrease in glycemia.