BACKGROUND: General medical and accident and emergency (A&E) services are the two major providers of open access out-of-hours care, and there are widespread concerns about rising and non-urgent demand presented to both. METHODS: This paper examines the differential use of these services out of hours, in an audit and research study two A&E departments and 21 practices in South London. It focuses on aspects of demand, including time of contact, age-related usage and nature of presenting complaints. Through interviews with a subsample of 82 patients who attended A&E, it also provides a more qualitative focus on differential decision making. RESULTS: Findings show that there are differences in the way A&E and general medical services are used in terms of age-related demand and aspects of presenting complaints. Significantly more families with children aged under 10 contacted a GP, and whilst more digestive, respiratory and viral/non-specific complaints were presented to GPs, musculoskeletal problems constituted the largest category of complaints presented at the A&E departments. However, some usage relating to perceived and actual availability of services appeared to be interchangeable in terms of site-of-help seeking. CONCLUSION: There is a need for a collaborative multi-method approach to respond to and influence demand.