OBJECTIVE: To identify patient and attendance characteristics that are associated with onwards referral to co-located emergency departments (EDs) or other hospital specialty departments from general practitioner (GP) led urgent care centres (UCCs) in northwest London, England. METHODS: We conducted a retrospective analysis of administrative data recorded in the UCCs at Charing Cross and Hammersmith Hospitals, in northwest London, from October 2009 to December 2012. Attendances made by adults resident in England were included. Logistic regression was used to model the associations between the explanatory variables-age; sex; ethnicity; socioeconomic status; area of residence; distance to UCC; GP registration; time, day, quarter, year; and UCC of attendance-and the outcome of onwards referral to the co-located EDs or other hospital specialty departments. RESULTS: Of 243 042 included attendances, 74.1% were managed solely within the UCCs without same day referral to the EDs (16.8%) or other hospital specialty departments (5.7%), or deferred referral to a fracture, hand management or soft tissue injury management clinic (3.3%). The adjusted odds of onwards referral was estimated to increase by 19% (OR 1.19, 95% CI 1.18 to 1.19) for a 10 year increase in a patient's age. Men, patients registered with a GP and residents of less socioeconomically deprived areas were also more likely to be referred onwards from the UCCs. CONCLUSIONS: The majority of patients, across each category of all explanatory variables, were managed solely within the UCCs, although a large absolute number of patients were referred onwards each year. Several characteristics of patients and their attendances were associated with the outcome variable.