Introduction: Ureteropelvic junction obstruction (UPJO) is associated with inadequate urine drainage from renal pelvis into ureter. UPJO results from incomplete recanalization of proximal ureter during fetal period which finally leads to hydrostatic distention of renal pelvis and calyces. Diagnosis is based on clinical symptoms, ultrasound, and diuretic isotopic renogram. Various surgical methods are used for treatment including dismembered pyeloplasty which is associated with better outcomes.Methods: Patients with UPJO who were undergone pyeloplasty (in an interval of 2.5 years) were followed and their pre- and postoperative ultrasounds and diuretic isotopic renograms were compared in terms of renal pelvis AP diameter in ultrasound and renal flow rate after injection of diuretics in renal scan.Results: Of 22 patients included in this study, postoperative renal pelvis AP diameter and renal flow rate were reduced in one patient, who then underwent reoperation with a diagnosis of recurrence. Despite normal postoperative renal flow scan, renal pelvis AP diameter in ultrasound had no significant change after surgery than before surgery in 4 patients (mean change 0.5 mm). Pelvis AP diameter was slightly increased in 2 patients (mean change 1.8 mm). Pelvis AP diameter was increased in the remaining 15 patients after surgery (mean 11.3 mm). Renal flow was increased following administration of diuretics in all patients (P<0.001).Conclusion: The present study showed that ultrasound based on renal pelvis AP diameter cannot definitely predict outcomes of patients with UPJO and renal scan is a reliable tool for evaluation of patients clinical and renal function improvement.