Fifty-one children with insulin-dependent diabetes mellitus (IDDM) and 24 healthy sibling controls were compared on one of two temperament questionnaires completed by parents. Children with IDDM did not provide a characteristic temperament profile or show any problem areas. A regression analysis to predict diabetic control as measured by most recent glycosylated hemoglobin (HbA1c) values revealed that five of the nine temperament scales accounted for a significant 42% of the variance in HbA1c (P less than .001). Children with higher activity levels, greater regularity in routines, milder reactions to external stimuli, distractibility, and negative moods were achieving better glycemic control. The results are discussed in terms of how individual differences in behavioral organization, energy consumption, and stress modulation may affect blood glucose levels.