WE REPORT EXPERIENCE with 16 patients undergoing spiral CT Scans for the evaluation of cerebral aneurysms. There were 10 females and six males, aged between 36 and 73 years. The three-dimensional scanning was useful in five situations: (i) Suspicion of aneurysm on conventional scan. An aneurysm was found in one of four patients and later confirmed by angiography, and two showed arterial ectasia with no saccular aneurysm; the fourth again appeared to have an aneurysm, but this was not shown on angiography. (ii) Follow-up of previously detected aneurysms not planned for surgery. This has been done in three patients, the spiral CT findings correlating well with previous angiography. (iii) Follow-up of aneurysm remnants after surgery (three cases); findings correlate well with previous angiography, and clips cause no artefact problems. (iv) Detection of ruptured aneurysms. In two cases, small aneurysms were found that had been missed on angiography, and in a third, with doubtful angiographic findings, spiral CT was useful. (v) Investigation of patients with past treated aneurysms, or of relatives. Three subjects have been screened so far for that purpose; in one a small aneurysm has been found, and confirmed angiographically.