The objective is to determine whether corticosteroid administration before biopsy prevents histopathological diagnosis of primary central nervous system lymphoma (PCNSL). A retrospective review was performed of immunocompetent PCNSL patients from 1985 to 2005. A total of 109 patients was identified. Sixty-eight (63.6%) patients received corticosteroids before diagnosis. Thirteen patients (of 109; 12%) had undergone repeat brain biopsy to confirm PCNSL. These included 8 (of 68) patients who had received corticosteroids (12%), and 5 (of 39) who had not (13%) (p = 1.0). The majority of PCNSL patients who received corticosteroids before diagnosis did not experience significant radiographic change or require second biopsy for diagnosis.