A non-invasive Stereoadapter was used for stereotactic CT-guided percutaneous brain biopsy in 18 patients with 16 solid tumours and four cysts. The Stereoadapter was mounted on the patient's head using ear plugs and a nasion support. After the CT study, the Stereoadapter was detached. The target was simulated on a phantom base and a probe carrier attached to the Stereoadapter. For surgery, the Stereoadapter with the probe carrier was remounted to the patient's head. Local anaesthesia was mainly used. Tissue samples were aspirated with a 2 mm diameter Sedan-Nashold biopsy cannula, introduced through a twist drill hole. Conclusive histological/cytological diagnosis was obtained in 16 of the 20 lesions. The new method proved to be reliable and quick. Since the imaging study and the surgery could be separated in time and place, the biopsy procedure was less time-consuming than previous methods of stereotactic biopsy using an invasive frame.