This paper examines spatial variation in the delivery of out of hours care through general practice, in two Health Authorities in north-west England. It demonstrates considerable variations in the type of care provided to patients in different parts of the region. These differences are not due primarily to either the geographical or socio-economic characteristics of the areas. Rather, the type of out of hours care delivered depends much more on variations in the structure and organization of service delivery. These factors, in turn, largely reflect the history of service development in each area and the ethos of individual GPs instrumental in establishing the service.