BACKGROUND: The reorganized out-of-hours general practitioner (GP) service, resulting in the creation of out-of-hours cooperatives has been widely welcomed by the medical profession. However, GP satisfaction remains only one aspect of this reorganized service and patients' views and levels of satisfaction must have a contribution to make to the organization and delivery of the service. AIM: To assess patient satisfaction at two out-of-hours cooperatives in Northern Ireland. METHOD: A sample of 4466 patients contacting the out-of-hours service was surveyed by postal questionnaires using a previously validated patient satisfaction instrument. RESULTS: Patients who initially requested to be seen at the out-of-hours centre were more likely to receive the contact they requested than those who requested telephone advice or a home visit. Only 41.8% of patients requesting a home visit actually received one. Patients were generally satisfied with the service provided and most satisfied with the 'doctor's manner' and the 'explanation and advice' received. Patients who received the contact they initially requested were more satisfied with all aspects of the service than other patients. The type of contact actually received had little effect on the satisfaction levels reported by patients who received the contact they initially requested. CONCLUSION: The population should be made fully aware of the services provided by out-of-hours cooperatives to enable them to have realistic expectations. With realistic expectations, patients are more likely to receive the medical contact they request and consequently will be more satisfied with the service provided. High satisfaction level is an important outcome measure of any out-of-hours service as it increases patient confidence and compliance and ultimately clinical outcome.