In this study, the possibility of non-invasive, three-dimensional demonstration of aneurysms of the basal cerebral arteries by means of spiral CT was investigated. The first step was to obtain exact definition of optimal examination parameters. Angio CTs at appropriate levels were performed on 10 subjects and time/density curves of the arterial and venous phases obtained in order to optimise the beginning of the arterial spiral CT series. The second step in this investigation was to examine 7 patients; in 6 of these basal aneurysms had been demonstrated by DSA. By means of multiplanar three-dimensional reconstruction from the data of the spiral CT it was possible to demonstrate 7 aneurysms with a diameter between 5 and 18 mm. Their position and relationship to the bony skull was also shown.