In 477 children with IDD treated by conventional methods, GHb (microcolumn chromatography) and a simultaneous random blood glucose concentration were measured over an 18-month period as indicators of metabolic control (once in 61 children, twice in 99, three or more times in 317). The data were analyzed to assess the effects of patient's age, sex, disease duration, and, in a random subgroup of 273, the number of daily insulin injections and insulin dose (U/kg). The mean +/- SEM percent GHb over this period was 11.8 +/- 0.2% and blood glucose concentration 237 +/- 9 mg/dl. Only seven children (1.4%) had a normal GHb value. There was a highly significant correlation between GHb and both age and blood glucose concentration but not with disease duration greater than one year. The correlation with age was present only in the girls. In 416 children evaluated more than once, with a mean duration between initial and most recent evaluations of 11.3 months, GHb remained within +/- 1% of the initial value in 40.5%, decreased in 32.3%, and increased in 24.2%. These data indicate a closer relationship between metabolic control in children with IDD and age of the child, particularly in females, than with disease duration. In our clinic, using conventional therapeutic methods, the ability to improve control over the short term as measured by changes in percent GHb has been quite limited. This study helps to target those IDD children, especially adolescent girls, requiring a more aggressive therapeutic approach.