The objective of this paper is to describe variations in the different models of out of hours general medical services and identify explanations for variation and the possible influence on patient satisfaction and service costs. A cross-sectional survey of all models of out of hours care was undertaken, including co-operatives, deputizing services, practice rotas and rural general practitioners doing their own cover. Fifteen sites were chosen representing 10 models of care, for more detailed case study; 65 semistructured interviews with key informants were conducted within the case study sites. A postal patient satisfaction questionnaire and an economic analysis were also carried out. Out of hours organizations have developed in response to a complex mix of the population served, geography, resources available and political expediency, leading to considerable structural heterogeneity, even within co-operatives. There was little evidence of formal integration with other services. Only the largest co-operatives showed any evidence of utilizing guidelines/protocols or of providing formal staff training. There were clear differences in the structure of out of hours care in urban and rural areas. Increasing the use of centralized call handling and triage will not address the needs of rural GPs, who would still be required to be available for work. Neither patient satisfaction nor costs varied bymodel of service provision. The English out of hours reviewhas outlined an integrated model of service provision with consistent standards within an accountability framework. It would appear that only the largest organizations will be in a position to address these standards and that they are likely to be inappropriate to the needs of GPs in rural areas.