The present study conducted risk-adjusted analyses to investigate the impacts of hospital and surgeon volumes on postoperative complications and the modified Rankin scale (mRS) after intracranial clipping of unruptured aneurysms, and to discuss the efficacy of relevant policy changes. Among 107 Japanese institutions, physician-reported data for 702 unruptured aneurysm patients were registered between December 2006 and April 2007. Postoperative complications and the mRS at the time of discharge were independently regressed against hospital and surgeon volumes, aneurysm size, aneurysm location, and comorbidities. Aneurysm size was a significant predictor of the overall outcomes. After adjusting for prominent confounders, hospital volume did not show any significant associations with postoperative complications (odds ratio [OR] 0.75, 95% confidence interval [CI] 0.34-1.68, p = 0.49) or the mRS (OR 0.60, 95% CI 0.19-1.93, p = 0.39). Higher surgeon volume (>or=100) was associated with lower mRS scores (OR 0.40, 95% CI 0.20-0.83, p = 0.013), but had no significant relationship with postoperative complications (OR 0.72, p = 0.47). Our risk-adjusted analyses showed no significant relationships between hospital volume and comorbidities. Therefore, the justification for hospital volume-based policies remains unclear. Prospective risk-adjusted volume-based studies are required for future evidence-based referral policies.