OBJECTIVES: Comparative analysis and productivity measurement of outpatient care, provided and reimbursed by IKA, the largest National Social Insurance Institution in Greece. In-house services of Patission Local Health Unit (LHU)) are compared to Family Doctor's private surgeries' medical visits (out-sourcing services). METHODS: A prospective study of medical visits for a 6 month period ( September 1, 2002 to February 28, 2003). Sample consisted of 23,982 outpatient visits to 3 specialities (5 Cardiologists with 12,538 visits, 3 Surgeons with 4,544 visits and 3 Otolaryngologists with 6,900 visits) offering their services in a LHU and 3 family doctors with 17,295 visits, belonging to the same LHU but offering their services in their private surgeries with 2,942, 8,245, and 6,105 visits respectively. Clinical and economic data is derived from IKA's Central Administration, its Information System, from LHU and interviews with executives. RESULTS: Productivity among all doctors presented significant divergences. The productivity of family doctors in their private surgeries was higher than LHU's doctors while the average waiting time appeared to be higher for medical visits to LHU's doctors. Average cost of medical visits to the LHU was estimated at 8.48€ while cost per speciality was 7.19€ for the cardiologist, 10.43€ for the surgeon and 7.83€ for the otolaryngologist. Average cost per visit to family doctors was 2.33€, while cost per specialty was 3.69€, 1.53€ and 1.77€ respectively. CONCLUSIONS: Average cost of medical visit to family doctor's private surgery was lower than the cost of medical visit to LHU's. The provision of outpatient medical care offered by IKA through out-sourcing seems to be most cost-effective. Economic evaluation studies, combining the efficient use of health resources with the adoption of effective patterns of patients' management, should be conducted at national level by all social funds and incorporated in their decision making process.