In order to evaluate vesicourethral dysfunction in diabetic patients, urodynamic studies, IVP and urinalysis were performed on 173 diabetic patients (male 78, female 95) and 17 nondiabetic control cases. In addition to the classical findings as increased volume at the first desire to void and decreased maximum vesical pressure, diabetic patients showed varieties of vesicourethral dysfunctions such as overactive bladder (14.5%), low compliance bladder (11.0%) and loss of detrusor-external sphincter coordination (31.7%). Vesicourethral function of diabetics was classified in following 5 types by analysing the volume at first desire to void, volume at maximum desire to void, maximum vesical pressure, residual urine volume and bladder compliance. 1. Type 1, normal vesical function, 13 cases. 2. Type 2, vesical dysfunction with minimal residual urine, 49 cases. 3. Type 3, vesical dysfunction with residual urine, 66 cases. 4. Type 4, low compliance bladder, 20 cases. 5. Type 5, overactive bladder, 25 cases. Pyuria was observed in 59.8%, hydronephrosis was found in 10.9% and ectasia of lower ureter was found in 17.8% of diabetic patients. The highest incidence of pyuria and abnormality of the upper urinary tract were noted in Type 4 and followed by Type 3 and by Type 2 in decreasing order. Extent of pyuria and ectasis of the upper urinary tract showed statistically significant correlation with residual urine volume and detrusor-external sphincter coordination. When vesicourethral function was compensated by abdominal strain, the volume of residual urine is not elevated, but when the mechanism of compensation is lost or in the absence of detrusor-external sphincter coordination results in gradual accumulation of residual urine. In cases with long standing chronic urinary tract infection may results in fibrosis of the bladder wall with low compliance bladder. Fibrotic obstruction of uretero-vesical junction can cause hydroureteronephrosis and followed by renal function impairment. As vesical damage become irreversible at this end stage, proper management during early stage is crucial for management of diabetic patients. Cholinergic agent were effective to reduce residual urine volume in Type 3. alpha-blocking agent were effective to reduce residual urine volume in Type 3 and some cases of Type 4. In cases in which medication therapy failed to reduce residual urine, the clean intermittent catheterization was successful in control of urinary tract infection and upper urinary tract ectasis. Transurethral resection of the prostate and the bladder neck is indicated in the male patients with a large amount of residual urine in Type 3 and 4.