OBJECTIVE: Adults with type 1 diabetes may have abnormal alterations in heart rate variability (HRV) due to cardiac autonomic neuropathy. This prospective study was performed to determine whether HRV can be used to detect subclinical autonomic neuropathy in diabetic children. RESEARCH DESIGN AND METHODS: We examined five time domain and three frequency domain HRV indices determined from 24-h Holter recordings in 73 diabetic children and adolescents aged 3-18 years (mean 12.1 years) with a mean duration of diabetes of 55 months. The measures were compared with normal ranges. Z scores were established for each parameter and were compared with classic risk factors of other diabetic complications. RESULTS: Most HRV indices were significantly depressed in children aged > or = 11 years, and the levels of HRV abnormalities were significantly correlated with long-term metabolic control (mean GHb for 4 years) in that age-group. In younger patients, HRV indices were within the normal range and were not correlated with the level of metabolic control. Illness duration and microalbuminuria but not short-term metabolic control (most recent GHb) were also independently predictive of HRV abnormalities. CONCLUSIONS: These results suggest that early puberty is a critical period for the development of diabetic cardiac autonomic dysfunction. Therefore, all type 1 diabetic patients should be screened for this complication by HRV analysis beginning at the first stage of puberty regardless of illness duration, microalbuminuria, and level of metabolic control.