Objective: To explore the causes, prevention, and management of the complications during intracranial aneurysm embolization with controllable coils (mechanical detachable spiral, MDS; and Guglielmi detachable coil, GDC). Methods: Retrospective review of 120 cases with 125 intracranial aneurysms embolized with controllable coils from March 1995 to July 1999 was conducted. The 20 accidents (in 18 cases) including aneurysm rupture, over-embolization, protrusion of coil end into the parent artery, and thrombosis of the parent artery were analyzed. Results: Among the 20 accidents, there were 6 aneurysm ruptures, 6 over-embolizations (in 5 cases), 6 coil protrusions, and 2 thromboses (one was secondary to coil protrusion). The embolization-related mortality was 3.33% (4/120), the permanent neurological deficit was 1.67% (2/120), and the transitory neurological deficit was 3.33% (4/120). The occurrence and outcome of the complications were related to the embolizing technique, the pattern of aneurysm and its parent artery, the imperfection of embolic materials, and the observation and management during embolization. Conclusion: Skilled embolizing technique, better understanding of the angio-anatomy of an aneurysm and its parent artery, correct judgement and management during embolization, and improvement of embolic materials are beneficial to the reduction of complications and to the melioration of the outcome of complications.