INTRODUCTION: Most patients undergoing elective surgery in the UK are discharged from hospital on the same day. Despite this, there is a lack of UK patient-centred outcome measures relating to quality of recovery, pain and analgesic use. The POPPY study was a UK-wide prospective, observational study measuring short- and longer-term patient-reported outcomes following day-case surgery. This article is the second in a series and describes baseline characteristics to contextualise successive articles which explore outcome data. METHODS: Baseline data were collected from eligible consenting adults undergoing day-case surgery. Data included patient characteristics; pre-operative analgesic use; pre-existing pain surgical and anaesthetic details; and quality of life scores. Descriptive analysis was performed to provide baseline characteristics of the study cohort. RESULTS: A total of 9618 patients were eligible on screening from 199 sites, with 7839 eligible following exclusions. Unplanned admission following surgery was the most common reason for exclusion, affecting 1131/9618 (11.8%) patients. Unplanned admission was more likely with increasing surgical magnitude, frailty and higher ASA physical status. Some common operations had admission rates of > 50%. Pain at the site of proposed surgery was reported by 3060/7839 (39%) patients and this was chronic pain in 2387/7839 (30.5%). Opioids were taken at least daily by 885/7839 (11.3%) patients, 1109/7839 (14.1%) were receiving treatment for depression and 1039/7839 (13.3%) were receiving treatment for anxiety. Anxiety or depression was rated as moderate or worse in 1002/7839 (12.8%) patients. DISCUSSION: In the UK, over a third of patients presenting for day-case surgery are in pain, which is mostly chronic in duration. One in four have access to opioid medications and a little over one in 10 are using opioids daily. More than one in 10 do not receive their planned surgery as a day-case and readmission rates for day-case surgery do not meet suggested targets.