There is increasing interest in the literature regarding the use of SPECT (single photon emission computed tomography) with 201Tl in the evaluation of cerebral tumours. Thallium (201Tl) is one of the isotopes most commonly used in studies of the myocardium and in the diagnosis of various tumours. Normal brain takes up very little 201Tl, but in viable tumour tissue the 201Tl becomes intracellular and is rapidly cleared from the blood stream. Such cerebral tumour uptake is related to changes in the permeability of the blood-brain barrier, regional blood flow and transport by means of the Na(+)-K+ adenosine triphosphate pump. Once the SPECT images have been obtained following administration of the radioisotope, one can calculate the indices of early and of late uptake together with the retention index. The usefulness of SPECT in the preoperative detection of malignant expansive pathology, choice of tumour region during stereotaxic biopsy, control of tumour reproduction and their differentiation from post-radiotherapy necrotic tissue, and evaluation of chemotherapy in treatment of cerebral tumours are analyzed. Finally the application of SPECT in metastatic conditions and the differential diagnosis of expansive lesions is considered.