Endoscopic third ventriculostomy (ETV) for obstructive hydrocephalus has a failure rate of 20-50% in various series. The present study analyzes ETV failures in 72 patients over a 2-year period and attempts to outline a management plan. Of the 72 patients who underwent ETV, it failed in 13. Seven of these failures occurred within 1 month, and in 5 others, ETV failed after 1-2 months. Another patient had a delayed failure 2 years after the initial surgery. Upon clinical failure, MRI scans were performed in all patients using either T2 fast spin echo or two-dimensional phase contrast MRI techniques. Of these, no flow could be demonstrated in 12 patients, whereas in 1 patient, good flow was observed. Endoscopic exploration was undertaken in the 12 patients in whom flow could not be demonstrated. Of the 12 who underwent endoscopic exploration, a patent stoma was observed in 7, necessitating insertion of a ventriculoperitoneal shunt (VPS). In the other 5, the stoma had closed by gliosis and a repeat ETV was performed. In 3 of these patients, in addition to the ETV, a VPS was also inserted in accordance with the family's wishes. VPS insertion was carried out in the patient with suggestion of good flow through the stoma. In failed ETV, MRI with flow studies is essential to identify the possible cause of failure. Endoscopic exploration is indicated for patients with no evidence of flow. A repeat ETV is indicated in patients with a closed stoma. Patients with a patent stoma could require insertion of a cerebrospinal fluid shunt.