A 63-year-old man with a history of chronic lymphocytic leukemia and a prosthetic aortic valve was hospitalized because of a mastoiditis, complicated by meningitis and epileptic seizures. Two weeks later he developed a lesion in the right temporal lobe. A brain abscess was suspected. However after treatment his clinical condition failed to improve. 99mTc-Tetrofosmin brain SPECT was performed and revealed substantially increased tracer uptake. Due to the patient's clinical deterioration, surgery was considered most appropriate. Histopathology established the diagnosis of glioblastoma multiforme. This case suggests a note of caution in every case of a rapidly evolving space-occupying lesion independently of the patient's previous history.