A case with an ill-defined arteriovenous malformation in the parieto-occipital region is presented. Open surgery was unsuccessful in removing the AVM totally, and treatment with gamma knife radiosurgery was then attempted. At 14 months after this treatment the AVM was believed to be obliterated. The patient had a new intracranial haemorrhage 59 months after radiosurgery. Renewed angiography showed an obvious AVM outside the previously irradiated area. Retrospective analysis of the angiogram at 14 months after radiosurgery revealed early filling of a draining vein as a sign of residual AVM at this time. Renewed radiosurgical treatment was performed. It is believed that an ill-defined margin, laminar flow, and effects of previous surgery might add to difficulties in a proper visualisation and delineation of an AVM. Further, a small remaining shunt may be overlooked if the angiogram is not carefully analysed or if the angiogram is of inferior quality. It should be stressed that partial or almost total obliteration of an AVM is no protection against rebleeding.