Forty-one patients with brain lesions underwent brain biopsy using either a computerized tomography (CT)-guided stereotactic approach or an ultrasound-guided technique. The cases were selected according to location and size of the mass lesion. Lesions 15 mm or less in diameter and those in the posterior fossa were biopsied by a CT-guided stereotactic technique (18 patients). Supratentorial lesions with a diameter larger than 15 mm were approached using ultrasound guidance (23 patients). These criteria for procedure selection provided a diagnostic yield of 94% for the CT-guided procedures and 91% for those guided by ultrasound. Safety for the two procedures was similar. The ultrasound procedure was more rapid, simpler, and less costly to perform. It is concluded that, with the protocol described, CT-guided stereotactic procedures could be reserved for cases in which absolute accuracy is mandatory.