Sixty complications occurred during 138 courses of intraarterial thrombolytic therapy in 122 patients during a 5-year period. These complications were recorded and analyzed prospectively to identify underlying errors in management. There were 31 bleeding episodes, 15 vascular complications, and 14 other complications. Twelve of the bleeding episodes occurred at the puncture site, and 19 occurred at remote sites, accounting for six of the eight deaths in the series. Management errors were clearly identified in 27 of the 60 complications. The three following patterns of errors were recognized: (1) mismanagement of bleeding (12 instances), (2) wrong patient selection (nine instances), and (3) breach of the administration protocol (six instances). The group of 27 complications with underlying management errors included seven of the eight deaths in the present series. Efforts to prevent complications from thrombolytic therapy should concentrate on the specific patterns of management errors identified. This study indicates that low-dose intraarterial thrombolytic therapy is not a low-risk alternative to surgical intervention but should be viewed as a prelude or possible alternative to surgery in selected patients despite the risks involved.