For many patients, pain is the most important outcome of any endodontic intervention. Despite our best efforts to perform technically ideal procedures, how much post-operative pain will be experienced and for how long is often unpredictable. Here we will discuss findings from a prospective study that measured post-operative pain intensity and duration after root end resection surgery. Risk factors identified in this study will be discussed and given context through the discussion of established risk factors for worse pain outcomes after surgery. We will also describe individual cases where the pain did not resolve after surgery and discuss whether these cases should be categorized as chronic post-surgical pain.