The authors previously reported an increase in the incidence of diabetes mellitus among Rochester, Minnesota, residents during the period 1970-1989. This study provides updated rates from data collected through 1994. Trends in diabetes surveillance, i.e., the proportion of residents who had a blood glucose measurement in each year between 1987 and 1994, are also provided. The authors reviewed medical records to identify residents aged 30 years or more who first met National Diabetes Data Group criteria for diabetes between January 1, 1970, and December 31, 1994. Age- and sex-adjusted incidence rates were calculated for successive quinquennia (5-year periods), and Poisson regression was used to test for an effect of calendar year; calendar period (1970-1989 vs. 1990-1994) was added to assess whether the association with calendar year varied in the most recent quinquennium. Altogether, 1,992 Rochester residents first met National Diabetes Data Group criteria for diabetes between 1970 and 1994. The age-adjusted incidence per 100,000 person-years increased 67% for males (267.0 vs. 444.8) and 42% for females (225.4 vs. 319.1) between 1970-1974 and 1990-1994. Calendar year (p < 0.001) and calendar period (p = 0.026) were significant, suggesting that rates accelerated during 1990-1994. The proportion of residents with at least one blood glucose measurement per year was unchanged (p = 0.181) from 1987 to 1994, while the incidence of diabetes increased (p = 0.033). Thus, the authors conclude that the increase in diabetes incidence accelerated over the last quinquennium and was not due to increased surveillance.