The aim of this study is to document the perioperative opioid use and its safety in the UK and countries in Europe and to describe its association with surgical complications, persistent pain and quality of life. In an international, prospective, observational cohort study, data about the perioperative pain management will be collected in all eligible hospitalised adult patients who undergo surgery in a designated study week in as many hospitals as possible in Europe. Baseline data will be collected, and participants followed up at one week, and at three and twelve months post-operatively. The primary outcome will be opioid use at three months after surgery. Secondary outcomes will include opioid use during the preoperative month (preoperative use), during surgery and up to one week after surgery (or discharge, whichever is earlier), and up to the end of the postoperative year. Additional secondary outcomes are the incidence of preoperative pain, persistent pain with/without the presence of neuropathic components, quality of life and surgical complications. The potential association between opioid use and pain outcomes will be investigated. This study could help to develop strategies to improve quality of care, through pain management, for patients undergoing surgery.