Purpose: In order to help identifying the subgroups of primary megaureter who neck operation, we retrospectively reviewed the clinical records of the patients who had primary megaureters without vesicoureteral reflux. Materials and Methods: We analyzed the initial differential renal function, UTI rate and the incidence of breakthrough infection of each group. Every patient had abdominal renal ultrasonograms and diuretic renograms during his/her follow-up period and the calyceal changes and differential renal functions were assessed. Results: Those who underwent operation in their neonatal period did not have considerable postoperative problems. Those with primary obstructive megaureters who underwent operation had severe calyceal dilatation at the initial evaluation. However, there were severe calyceal dilatation in the nonobstructive-nonrefluxing group, too. Those who had poor differential renal function at the initial evaluation had a greater chance to have surgical correction. Those who were classified as primary obstructive megaureter and underwent operation had a higher rate of urinary tract infection than the counterpart who had consevative care. Conclusions: In order to differentiate those who need operation, we think that the differential renal function, the calyceal morphology, The diuretic renogram curve and urinary tract infection all act as combined factors altogether and not a single factor acts as a contributing factor. That is, if the diuretic renogram cutie is obstructive and there is urinary tract infection in the initial evaluation or if there is severe calyceal dilatation and decline of the differential renal function, we think that surgical correction should be under consideration. In contrast, if the diuretic renogram cutie is not obstructive and there are other factors combined, we think that conservative treatment should be the choice only if there is no breakthrough infection.