Cerebrospinal fluid hydrothorax is reported as a rare complication of ventriculoperitoneal (VP) shunt. A 16-month-old boy known to have congenital hydrocephalus and a Dandy-Walker cyst presented with serious respiratory distress. Examination revealed right pleural effusion and congested throat. Thoracocentesis with drainage of the pleural cavity for 10 days failed to free the patient from pleural effusion. Following an intraperitoneal injection of Omnipaque a chest X-ray was done, and samples of pleural fluid taken before and after the injection were compared on X-ray, revealing the presence of contrast in the postinjection pleural effusion. Changing the VP shunt for a ventriculo-atrial shunt resulted in immediate (within 1 day) complete disappearance of the pleural effusion and of the patient's chest symptoms. Probable causes of this rare complication are discussed, and attention is drawn to the possibility of its appearance and early recognition. Intraperitoneal injection of contrast material followed by X-ray examination of fluid in the chest is a simple, safe, and reliable method of diagnosis when it is suspected.