The present study aims to evaluate the effect of desmopressin treatment on urine output, density and glomerular filtration rate (GFR) in patients with posterior urethral valve (PUV) and the factors affecting the response to this treatment.A total of 68 PUV patients who were followed-up after valve ablation were examined with the fluid intake, urine output and GFR. Sixteen patients who were polyuric (a urine output more than 30 ml/kg/day) and had hypoosmolar urine (urinary density of 1015 or lower) included in the study. Blood chemistry and serum ADH level were studied. Following 5 days of observation, patients were given DDAVP perorally with a dosage of 0.4 mg/day, two equal doses per day. After 7 days and after a 3 month period of treatment, voiding characteristics, day-time and night-time urine densities and also GFR have been re-evaluated.The mean age was 6.8 years (range 2 to 11 years). The mean age at valve ablation was 20.7 months (range 5 months to 6 years). The mean daily urine output during first week and at the third month of the treatment had decreased significantly (p=0.004 and p=0.006). There was increase in night-time and day-time urine density in 10 patients (62%) and in 13 patients (81%) respectively at the third month evaluation. Increments in urine density were statistically significant for the third month evaluation. Nine (56%) patients had ADH levels within normal (7 pcg/ml) levels and 7 patients had higher levels. There was no statistically significant difference between pretreatment and posttreatment micturation characteristics. However patients with voiding dysfunction responded better to DDAVP treatment.Desmopressin treatment improves polyuria in PUV patients. The responses are better particularly in PUV patients with significant bladder dysfunction. This supports the harmful role of polyuria on bladder dysfunction. The DDAVP treatment improves the day-time and night-time in PUV patients. Combination of DDAVP treatment with overnight catheterization may be a good alternative that needs to be evaluated by further prospective randomized studies.