Computer analysis of complications of 5,000 catheter cerebral arteriograms performed at four hospitals (two training and two nontraining) revealed a total of 68 complications (1.4%). Eight (0.16%) of these complications were major: five patients required thrombectomy or embolectomy, two had permanent neurologic deficits, and one patient died. The complication rate for the training hospitals (3.9%) was significantly higher than that for the nontraining hospitals (0.9%), but the rates of permanent complications were identical in both groups (0.1%). Reporting criteria and complication types are described.