&NA;Despite the widespread availability of image‐guided stereotactic biopsy, the need for such procedures in patients with “clear‐cut” clinical and radiographic diagnoses is still frequently discussed. In an attempt to ascertain the incidence of unexpected pathological findings, 100 consecutive stereotactic biopsies have been reviewed. Twelve patients were found to have diagnoses of pathological conditions that preoperatively were considered unlikely, or not considered at all. The details of these “diagnostically discordant” cases are discussed. (Neurosurgery25:180‐184, 1989)