Classic research has demonstrated a link between increased surgical volume and improved patient outcomes at the hospital level. This research has raised interest in systematic referral of certain procedures to specialized centers, and the Leapfrog Group included volume-based referral as one of its recommended safety practices. However, this study finds that the volume–outcome relationship is limited to a few specific surgeries, and that wide overall variation in surgical mortality exists even after controlling for volume. The authors argue that given these findings, systematic volume-based referral is unlikely to improve surgical outcomes.