A 12-year-old patient developed prolonged nondilated urinary obstruction and pleural effusion shortly after undergoing renal transplantation. Renal sonography, angiography, and isotope renography failed to identify an obstructive process. On the 18th postoperative day, pleural effusion was noted in the right hemithorax, and by day 24, increased perinephric fluid was observed on renal scan. Following a nephrostomy, the pleural effusion resolved and renal function improved remarkably. A ureterovesical junction obstruction and renal pelvis tear that were later discovered were repaired. Whenever a ureteral obstruction is suspected the diagnosis should be pursued vigorously, despite normal radiologic findings, especially in the presence of pleural effusion. Consideration of the possibility of urinothorax in such cases may obviate the need for lung biopsy.