Twenty-four insulin-dependent diabetic children and 114 normal control children, all between the ages of 6 to 16 years, were investigated for riboflavin deficiency. The method used was a measurement of erythrocyte glutathione reductase activity and the results were expressed as the activity coefficient (AC). None of the children had received vitamin supplementation. The percentage of diabetic children with riboflavin deficiency was 4 fold greater than in non diabetics. Supplementation with daily oral riboflavin quickly returned all AC values to normal.