There is currently a lack of information on critical questions surrounding laterality of ureteropelvic junction obstruction (UPJO), the difference between extrinsic and intrinsic obstruction, the utility of retrograde pyelogram, and the appropriate management for patients with concurrent UPJO and ureterovesical junction obstruction (UVJO). Therefore, we propose first a retrospective study of all pyeloplasty’s completed at CHLA for UPJO to answer some of these critical questions. The results of this study may inform future studies in this realm. We will retrospectively review all cases of pyeloplasty completed at CHLA (from 2000 through present) to identify differences in outcomes.