Abstract Purpose We evaluated urinary transforming growth factor-beta 1 (TGF-beta 1) concentration in children with upper urinary tract obstruction as a potential tool for supporting the diagnosis of clinically significant obstruction. Materials and Methods Renal pelvic and bladder urine samples were obtained for analysis from 30 patients a median of 5 months old who underwent surgery for obstruction at the ureteropelvic (29) and ureterovesical (1) junctions. Urinary TGF-beta 1 concentration was measured using a quantitative sandwich enzyme-linked immunoassay technique. Bladder urine TGF-beta 1 in patients with obstruction was compared with that in controls. In addition, we compared renal pelvic and bladder urine TGF-beta 1 in patients with obstruction. Results Mean bladder urine TGF-beta 1 plus or minus standard error of mean was 4-fold higher in patients with upper tract obstruction than in controls (195 +/- 29 versus 47 +/- 7 pg./mg. creatinine, p <0.001). In the obstructed group mean TGF-beta 1 in the renal pelvic urine was 378 +/- 86 pg./mg. creatinine, or twice that of the bladder urine (p = 0.02). Conclusions Bladder urine TGF-beta 1 in patients with upper urinary tract obstruction is significantly elevated compared with that in controls. To our knowledge our study is the first to identify a bladder urinary marker that correlates with upper urinary tract obstruction with greater than 90% sensitivity. Measuring TGF-beta 1 in a voided bladder urine sample may provide an objective and noninvasive test for assisting in the diagnosis of upper urinary tract obstruction.