Post-operative pain is undertreated, in large part because it is often "invisible." In the outpatient setting, pain can go unnoticed or disregarded by physicians, nurses and patients who consider it a natural and physiologic consequence of surgery. The problem is, post-op pain can profoundly hinder outcomes, and the failure to appropriately assess and treat pain is fast becoming a liability issue. In this article, I outline an evidence-based approach that will help you bring some accountability and objectivity to the process of pain assessment.