The aim of this study was to determine the prevalence of and some risk factors for impaired glucose tolerance (IGT) in 2- to 5-yr-old offspring of diabetic mothers (ODM). The glucose tolerance of 51 offspring born to women with pregnancies complicated by diabetes (type 1) and of 109 children of the control group was analyzed. Our results showed that the fasting glycemia of ODM was similar, when compared to the controls, but 2 h after the glucose loading the glycemia of ODM was significantly higher than that in the control group (5.47 +/- 1.79 mmol/L vs. 4.86 +/- 1.13 mmol/L). Normal glucose tolerance was found in 68.6% of ODM and 86.2% of controls; IGT was found in 17.6% of ODM and 4.6% of controls. Children with macrosomia at birth or overweight at 2-5 yr had IGT at 2-5 yr more often than children with normal weight at birth or normal weight at 2-5 yr. A significant, though relatively low, positive correlation was found between the duration of breastfeeding and fasting glycemia (r=0.241, p <0.01), and positive correlation was found between the duration of breastfeeding and glycemia 2 h after glucose loading (r=0.458, p=0.002) in the offspring of diabetic mothers. In conclusion, the average glycemia of ODM after glucose loading was higher than that in the control group. Macrosomia after birth, overweight, and obesity in childhood had a significant influence on the glucose tolerance of the ODM. The results of the oral glucose tolerance test correlated with the length of breastfeeding.