Glucocorticosteroids (GC) play an important role in the treatment of neuro-oncologic patients. GC are used for the management of malignant brain tumors, either primary of secondary, neoplastic epidural spinal cord compression (NESC), as adjuvant chemotherapy of some central nervous system tumors and perioperatively in brain surgery. GC are believed to exert their influence on brain tumors mainly by reducing the tumor-associated vasogenic edema, probably by decreasing the increased capillary permeability of the blood-brain barrier (BBB). Experimental as well as clinical studies applying computed tomography, magnetic resonance and PET have supported these theories. However, other mechanisms have been proposed and investigated, such as a reduction of cerebral blood flow and oncolytic effects, the latter being controversial. The effect of GC is best observed in patients with cerebral metastases and gliomas. Studies on the effect of non-steroidal anti-inflammatory drugs (NSAIDs) gave conflicting results. Although some prefer methylprednisolone, dexamethasone is the GC given in the majority of neuro-oncologic patients, at an empirically chosen dosage of 4 mg qid. Dose-effect studies in patients with cerebral metastases as well as in patients suffering from NESC have been performed and lower doses in a twice daily regime may be sufficient. Side-effects may be divided in three groups: those originating from the mineralocorticoid activity, the withdrawal of the drug and the chronic excess GC administration. Steroid myopathy is the most frequent occurring serious side-effect in neuro-oncologic patients. Others include gastrointestinal perforation and hemorrhage, opportunistic infections, steroid diabetes, and skin and facial changes. The most important interaction is that with phenytoin. The influence of dexamethasone on the effects of chemotherapy and radiotherapy is also discussed. New developments in GC treatment include the local administration of dexamethasone.