Twenty-four hour BP and heart rate measurements were carried out in fourteen newly diagnosed-, and in twenty-eight diabetics with 5-13 years of duration; and in eight healthy control children. Mean arterial BP rose at night in five-, fell slightly (less than 10%) in five- and fall markedly (more than 10%) in eighteen diabetics with longer duration of the disease. The diurnal-nocturnal difference of mean arterial pressure was significantly lower in the groups with nocturnal BP rise and slight nocturnal BP fall, compared to the control group (< 0.001; p < 0.01, respectively). The diurnal-nocturnal differences of heart rates were significantly lower in diabetics with relative "nocturnal hypertension" compared to the control group (p < 0.05). The presence of subclinical signs of diabetic autonomic neuropathy was significantly higher in patients with nocturnal BP rise and slight nocturnal BP fall compared to patients with marked nocturnal BP fall and newly diagnosed diabetics (chi squared p = 0.02 and p = 0.01, respectively). In conclusion, the prevalence of autonomic symptoms in diabetic children could be related to change in diurnal/nocturnal arterial BP, however longitudinal studies of ABPM are needed to define, whether patients with abnormal BP profiles are candidates for the development of diabetic vascular disease.