The authors report the clinical and pathological findings in 201 procedures to revise malfunctioning ventriculoperitoneal shunts in 114 patients. The revised shunts were predominantly Raimondi three-piece systems. Collection of fluid along the shunt track is emphasized as an early clinical feature of shunt malfunction. In some cases, there are few clinical signs of shunt infection, and the first indication of it may be shunt malfunction. Ventricular catheter obstruction was caused by tissue from the region in addition to choroid plexus. Inflammation was frequently found around both ventricular and peritoneal catheters. Foreign bodies (cotton fiber, hair, and talc) and granulomatous inflammation were often present at both ends. Tissues obstructing the peritoneal catheter included embolic neoplastic cells, choroid plexus, and leptomeninges. There was also more necrotic debris at the peritoneal end. To prevent shunt malfunction, attention should be directed to: 1) optimal placement of ventricular catheters inside the lateral ventricle; 2) prevention of infection; 3) avoidance of contamination by cotton fibers, hair, or talc; and 4) improvements in the biocompatibility of the implanted materials.