DISCUSSION: The diagnosis of urinothorax requires a high degree of clinical suspicion. Pleural fluid analysis is commonly consistent with a transudate with pH less than 7.40 (1). However, when the pH is higher than 7.40, it tends to be in cases of urinary tract infection with ammonia producing and urease-splitting bacteria, such as proteus or klebsiella (2), or in this case, staphylococcus aureus. The most specific and definitive biochemical feature of an urinothorax is the presence of high pleural fluid creatinine levels and a pleural fluid/serum creatinine ratio greater than 1. Concurrent CT abdomen may reveal an ipsilateral upper genitourinary (GU) lesion with a retroperitoneal fluid collection (urinoma) communicating with the pleural space. Nuclear imaging using radionuclide technetium-99m-mercaptoacetyltriglycine-3 or technetium-99m DTPA (diethylenetriaminepentaacetic acid) scintigraphy confirms the diagnosis of urinothorax by demonstrating a leakage of the dye from the GU tract into the pleural space (3). Urinothorax resolves immediately upon relief of the obstructive uropathy.