789 patients with diabetes mellitus were studied by clinical and electroneurographical examination. Motor conduction velocity of the median and the tibial nerve and sensory conduction of the median nerve were determined. 81.1% of the patients we suffering from diabetes which began in childhood or adolescence, 13.9% were suffering from maturity onset diabetes. Average duration of the disease was 9.5 years, average age was 26.7 years. Clinical signs of polyneuropathy were found in 19.1%. Typical findings were pain and paraesthesia, lack or abolition of triceps surae reflexes, impaired pallaesthesia on lower extremities. 48.3% of 151 patients with clinical signs of polyneuropathy were suffering from combined angiopathy, 32.5% from microangiopathy, 7.9% from macroangiopathy. Severity of complicating retinopathy and macroangio,athy were found to be correlated with polyneuropathy. 58.2% of 323 diabetics with at least one delayed nerve conduction velocity exhibited signs of angiopathy. In nearly 30% of children and adolescents after comparatively short duration of the disease at least one conduction velocity was delayed. In diabetic children and adolescents metabolic disturbances are assumed to cause peripheral nerve dysfunction.