Complication rates in 5,000 consecutive catheter cerebral arteriograms were assessed with regard to arteries injected, contrast medium used, patient age, and duration of procedure. No statistically significant difference was found between the complication rate when the carotid artery alone was injected and that when the carotid artery was injected in combination with the vertebral artery, the aortic arch, or both. There was also no significant difference between the total complication rates using Conray-60 and Renografin-60. However, although Conray-60 demonstrated no change in complication rate with increased volume, Renografin-60 showed a consistent and significant increase in complication rate with increased volume. Complication rates were also significantly higher when the procedure lasted more than 80 min and in patients more than 40 years old. As might be expected, nontraining hospitals used significantly less contrast material and had significantly shorter procedures than training hospitals.