Since the first half of the last decade, numerous authors have testified to the clinical usefulness of corticosteroids in patients with brain tumors. The mechanism of benefit of these agents is controversial. Although it is clear that corticosteroid therapy reduces cerebral edema around brain tumors, mounting experimental evidence suggests that steroid compounds also may have a direct antineoplastic effect on brain tumor cells. The principal disadvantage of such therapy is that it makes difficult the evaluation of the tumor's response to oncolytic agents simultaneously administered. The most effective dosage of steroid varies; some patients require 96 mg dexamethasone daily before the maximum effect is achieved. These differences in response may be due to varying degrees of peritumoral edema, normal differences in steroid metabolism, and complex drug-to-drug interactions. Corticosteroid therapy may increase the incidence of gastrointestinal bleeding in neurosurgical patients, but this low risk is acceptable in view of its many advantages.