A cooperative study based on 1,112 patients was undertaken in order to ascertain whether computed tomography (CT) allows earlier diagnosis of brain tumors or not. The patients were divided into 2 groups. In the first group (pre-CT period; 552 patients) diagnosis was made without CT, in the second (CT period; 560 patients) with CT. Duration of symptoms, assumed as the interval between onset and definite diagnosis, was the main parameter considered. The most relevant results were: a) during the CT period a significant decrease in duration of symptoms before diagnosis was observed for meningiomas (from 21 to 13 months) and low-grade gliomas (from 16 to 9 months), while no significant change was recorded for high-grade tumors (from 4.6 to 3.5 months); b) during the CT period the figure for benign tumors operated upon rose to 44 per cent (pre-CT: 25%) balanced by a marked decrease in surgery for malignancies (from 43% to 23%); c) better indications for surgery were associated with a significant reduction in cases operated upon during the CT period (72% versus 79%, p less than 0.01).