OBJECTIVE The possible relationship between bladder dysfunction and autonomic neuropathy was investigated in unselected diabetic patients. METHODS Bladder function was examined by cystometry in 53 unselected diabetic patients and 10 healthy controls. Sympathetic skin response was recorded in 23 of 53 patients and all control subjects to evaluate autonomic neuropathy associated with diabetes, and the results were compared to cystometric findings. RESULTS Cystometrograms exhibited significant increases in bladder volume at first desire to void and maximal bladder capacity, and a decrease in detrusor contractility in diabetic patients compared to those in controls. In addition, mean residual urine was significantly larger in diabetic patients than in controls. Among the 53 diabetic patients these bladder dysfunctions were also found in each subset of patients with no sign of retinopathy (33), no subjective urinary symptoms (32) or duration of diabetes less than 1 year (12). In 23 patients in whom sympathetic skin response was measured 12 without sympathetic skin responses had increased residual urine and decreased detrusor contraction pressure. The remaining 11 patients with a lower amplitude of sympathetic skin response and more prolonged latency than controls had a significant decrease in detrusor contraction pressure. CONCLUSIONS Bladder dysfunction, characterized by loss of sensation, increased capacity and decreased contractility, was the main observation of diabetic cystopathy regardless of the duration or severity of the disease. The association of bladder dysfunction and autonomic neuropathy detected by the sympathetic skin response might indicate that diabetic cystopathy is a manifestation of peripheral neuropathy induced by diabetes.