Backround: Because of the dismal prognosis of untreated brain lymphoma early histological verification using stereobiopsy is decisive for patient with this disease. The study analysed the diagnostic yield of stereobiopsy in brain lymphoma patients with respect to prebiopsy corticosteroid administration. Patients and Methods: Patients with brain lymphomas were identified in a group of 162 stereotactic biopsies (108 frame-based and 54 frameless) of patients harboring suspected brain tumor. Non conclusive biopsies were reevaluated to exclude the possibility of missed lymphoma. Results: Total 9 patients (8.3%) and 4 patients (7.4%) had lymphomas in the frame-based and frameless stereobiopsy groups, resp. In 10 patients, corticosteroid treatment of perifocal brain oedema was conducted continually up until biopsy (including one patient with corticotherapy for pulmonary disease). Lesion regression was observed in 6 of these patients. Transient lesion remission was observed during corticotherapy in one patient with lesion recurrence after steroid discontinuation. In 2 patients, corticosteroids were not administered before biopsy. The results of stereobiopsy were inconclusive in 8 patients (4.9%). Before biopsy, the possibility of brain lymphoma was considered in 3 patients, but the final diagnoses were autoimmune vasculitis, histological changes after embolic events from the thrombosed pulmonary veins in pulmonary malformation and local inflammation. Conclusion: Although the extent of brain lymphoma decreased after corticosteroid administration, corticotherapy does not exclude valid diagnostic biopsy.