From January 1991 to 1994, 99 aneurysms in 91 patients were clipped in the Neurosurgy Department of Beijing Tiantan Hospital. Six residual aneurysms were found by postoperative angiography. We analyzed these patients and concluded that the occurrence of residual aneurysms depends mainly on the location, size, type, neck width of the aneurysms, and their rupture during operation. According to this, we give opinions on how to prevent residual aneurysms and how to deal with them.