One of the main problems regarding the follow up of patients with brain tumors treated with radiotherapy is the distinction between radiation necrosis and tumor relapse. In many cases CT and MRI are unable to distinguish between the two. We assessed the usefulness of Tc-99m MIBI brain SPECT in solving this problem. We studied 68 patients with primary brain tumors, before and after treatment, with a total number of 104 examinations. The results were concordant with the radiological examinations in 76 studies while discordant in 28 studies.