Urinothorax [UT], the accumulation of urine in the pleural space, is an uncommon cause of pleural effusions resulting from trauma, obstruction, or iatrogenic causes. Thoracentesis with pleural fluid analysis and evaluation of biochemical characteristics, such as pleural fluid creatinine (PCr) to serum creatinine ratio (Scr), is necessary to establish this diagnosis. This case illustrates a 93 year old man with a complicated past medical history including chronic kidney disease stage 4, adenocarcinoma of the prostate status post brachytherapy complicated by proctitis, high grade transitional cell carcinoma of the right kidney with right hydronephrosis, and recurrent hematuria who was hospitalized for worsening hematuria and suprapubic pain. The patients CXR showed a large right pleural effusion. A repeat thoracentesis was performed removing 1.85L clear yellow fluid. PCr and SCr were 4.1 mg/dl and 3.94 mg/dL respectively. This confirmed the diagnosis of UT with a PCr to SCr ratio of 1.04. Again, diagnosis requires pleural fluid analysis and is associated with a paucicellular, transudative effusion with an ammonia-like odor, acidotic pH less than 7.4, and a PCr to SCr ratio greater than 1.0. Management is dependent on correcting the underlying pathology, such as repairing traumatic GU injury or obstruction.