We report six patients with progressive primary tumors of the brain who had prolonged periods with stable contrast-enhancing CT lesions following initial responses to chemotherapy. Chemotherapy was discontinued after 21 to 36 months, despite the persistence of apparent disease in each patient. PET using (F-18) fluorodeoxyglucose was performed in three patients, revealing hypometabolic lesions. All six patients are alive and well, with no clinical or radiographic evidence of progressive disease at 24 to 57+ months following termination of treatment. The usual criteria for terminating phase I1 chemotherapy in patients with a recurrent brain tumor are evidence of progressive disease or unacceptable toxicity. However, chemotherapeutic success mandates that these criteria be expanded to include patients whose response following the initiation of phase II treatment is followed by prolonged (greater than 1 year) radiographic and clinical stability. Complete response, ie, disappearance of all evidence of disease, is unusual in patients with recurrent primary brain tumors, even with highly effective therapy. Continued improvement in the therapy of patients with these tumors will allow wider application of these criteria. © 1989 American Academy of Neurology.