During a 4-year period, four patients presented with transient disturbances in neurologic function that were diagnosed as seizures in two and transient ischemic attacks in the other two. Computed tomography (CT scan), both with and without contrast, was normal in all four patients. Isotopic brain scans (3 patients), cerebral angiograms (4 patients), and lumbar punctures (4 patients) were normal. Electroencephalograms (EEG) were normal in two patients and abnormal in two patients (consisting of focal slowing). Within 4.5 months, all patients developed symptoms and signs of a brain tumor, and in all four, CT scan now revealed a large mass lesion which at surgery was shown to be a malignant astrocytoma. These four patients constituted 4% of the total number of patients with malignant astrocytomas that were seen at the NYU Medical Center during this same time period. It is stressed that the CT scan may be normal early in the course of patients with brain tumors, particularly if they present with a transient disturbance in neurologic function. The first evidence of the tumor in such patients may be a slow-wave abnormality on the EEG. Patients who are suspected of having a brain tumor should, if the initial CT scan is normal, have the scan repeated later.