The relationship of 24-h glucose profiles to age, haemoglobin A1c (HbA1c), and C-peptide concentration was analysed in consecutive, unselected children who had developed Type 1 diabetes 2 years earlier. Seventy-seven children in four age groups (age 2-4 years, n = 9; 5-8 years, n = 14; 9-12 years, n = 26; and 13-17 years, n = 28) were studied. Each child was hospitalized for 2 days for the investigations. Mean blood glucose concentration was 9.7 +/- 4.1 (SD) mmol l-1 in children aged 2-4 years; 10.7 +/- 4.0 mmol l-1 in those aged 5-8 years; 11.3 +/- 3.4 mmol l-1 in those aged 9-12 years; and 9.8 +/- 3.3 mmol l-1 in those aged 13-17 years. Results were > 7.0 mmol l-1 in 69% (range 56-76%) and > 10 mmol l-1 in 49% (39-57%) of the measurements. Values decreased by 30% (21-43%) between 10 pm and 3 am. The nadir of the mean profiles of the groups was always at 3 am. Glucose concentration was mmol l-1 in 25% (14-50%), < 2.5 mmol l-1 in 9.6% (0-21%), and < 2.0 mmol l-1 in 2.7% (0-4.2%) of the children at 3 am; hypoglycaemia was most common in those aged 5-8 years. Of the four profile characteristics used, mean blood glucose predicted HbA1c (R2 = 24.7%, p < 0.00005, multiple linear regression analysis), and slightly more in combination with age (R2 = 32.0%, p < 0.00005).(ABSTRACT TRUNCATED AT 250 WORDS)