The presence of residual urine was determined by postvoid bladder ultrasonography in 37 control subjects and 102 unselected insulin-dependent and non-insulin-dependent diabetic patients. Significant residual volume was detected in 19 diabetic subjects without explanation other than diabetic neurogenic bladder dysfunction in 15. The four others had prostatic hypertrophy. Excluding these four subjects, those with residual urine were slightly older than the others (P less than 0.05), but the known duration of diabetes was increased only for the insulin-dependent group (P less than 0.05). The presence of residual urine was strongly associated with peripheral neuropathy (P less than 0.001). In contrast, of all the manifestations of autonomic failure studied, only impotence (P less than 0.01) and decreased pupil motility (P less than 0.05) were associated with residual urine. The prevalence of urinary tract infection was higher in women than in men (P less than 0.02). This prevalence was increased in the presence of residual urine (P less than 0.02) but only for men (P less than 0.001).