Glioblastoma multiforme is the most common primary brain tumor of adults, as well as the most malignant. Its etiology is unknown, but the tumor is thought to arise through dedifferentiation of adult astrocytes. It occurs most frequently between the ages of 40 and 60, in men more often than in women (1.5:1). Important early symptoms include subtle personality change, headache, weakness, and intellectual impairment; specific complaints and physical findings depend on the location of the lesion. The initial diagnostic test should be a CT-scan; it will detect more than 90% of malignant astrocytomas. Surgery remains the cornerstone of treatment; patients receiving radical debulking have a median survival of 8 months compared to the 3 month survival of unoperated cases. Modern neurosurgical technique, neuroanesthesia, mannitol, and corticosteroids have reduced the surgical mortality to 3%. Most patients also receive 4500 rads of whole-brain irradiation and 1800 rads to the operative site; radiotherapy increases the median survival of operated patients by 2 to 3 months. An additional small increment in survival time and some improvement in quality of survival can be achieved by nitrosourea chemotherapy; the latter is usually given as 100 mg/m2/day × 3 days of BCNU every eight to ten weeks. Experimental treatments under study include the use of radiosensitizers, the role of immunotherapy and the application of microwave-induced hyperthermia. Two-year survival remains 10% to 20%, and there are virtually no five-year survivors. An optimal combined modality treatment plan, one in which each cellular compartment of this truly multiforme tumor is effectively addressed, remains to be designated.