OBJECTIVE Transfemorally placed endoluminal grafts are currently being evaluated as an alternative to open surgery for the treatment of abdominal aortic aneurysms. We determined the value of helical CT for the follow-up of patients treated with this new procedure. The purposes of this study were to determine CT features of a technically successful procedure, detect complications, and compare findings on CT scans obtained 24-48 hr after insertion of the graft with findings on angiograms obtained at the end of the endovascular procedure. METHODS Seven patients with large abdominal aortic aneurysms had helical CT within 48 hr after transfemoral insertion of an endoluminal graft. Findings on these CT scans were compared with findings on digital completion angiograms obtained immediately after placement of the graft. Additional follow-up CT scans were obtained for up to 15 months (mean, 8 months). The size of the aneurysmal sac; completeness of perigraft thrombosis; and position, shape, and patency of the device were recorded. RESULTS CT scans obtained 24-48 hr after placement of the grafts showed complete thrombosis of the aneurysmal sac in three patients and incomplete thrombosis with patent perigraft channels in the four remaining patients. Angiograms showed a patent perigraft channel in only one patient. Two of four initially patent channels subsequently closed, but one of them recurred. Of four thrombosed aneurysms, two decreased in size, and two were unchanged on later follow-up. Of three aneurysms associated with perigraft channels, two became enlarged and one was stable. On the basis of CT criteria, successful endovascular repair was shown in four (57%) of seven patients. CONCLUSIONS Helical CT is a sensitive means of evaluating the efficacy of endoluminal grafts. Decreased or stable size of the aneurysmal sac without perigraft channels on late follow-up CT signifies technical success. Persistence or recurrence of perigraft channels is the most likely cause of later enlargement of an aneurysm and therefore suggests procedural failure. Helical CT was more sensitive than angiography for detection of perigraft channels that occurred soon after treatment.