We retrospectively investigated preoperative variables contributing to adverse surgical outcome for repair of unruptured posterior circulation aneurysms on data collected prospectively between October 1989 and March 2010. Putative risk factors including age, sex, smoking status, positive family history, modified Rankin Score prior to the surgery, size of the aneurysm, specific site (basilar caput and trunk, vertebral artery and posterior inferior cerebellar artery), midline location, presence of calcium, thrombus or irregularity in the aneurysm on preoperative imaging, associated arteriovenous malformation and preoperative coiling were investigated using regression analyses. In a total of 121 operations, surgical mortality and morbidity was 16.3%. For patients with aneurysms less than 9 mm this rate was 3.2%. Among the investigated variables we found that size, calcification of the aneurysm and age were each predictors of surgical outcome of unruptured posterior circulation aneurysms.