Many tertiary hospitals have started to establish cooperative relationships with small and medium sized hospitals in Korea. But the performance of the relationship is not satisfactory to both of partners. The relationship and performance of cooperation for small and medium sized hospitals are analyzed according to the framework of inter-organizational cooperation. Data are collected by 4 focal hospital and 34 small and medium sized hospitals through interview and questionnaire. The findings are : a) The cooperation is focused on management area, such as healthcare technology transfer and information sharing, rather than patient referral. b) Patient referral is not yet active in cooperative relationship. But some partner hospitals which is located close and managing internal organization for cooperation show a significant number of referrals. c) The characteristics of high performers are positive attitude about cooperation, and recognition of the relationship as flexible, experiences of cooperation, internal and external management activities.