Objective : To empirically investigate the relationship of internal and external customer satisfactions, service quality, and customer loyalty in medical services. Methods : This essay proposes an integrated model to explain the causality of internal and external customer satisfactions, service quality, and customer loyalty. To this end, a structural model was developed, consisting of the following factors: internal and external customer satisfactions, service quality, and customer loyalty. The study included 214 sets of data, with 107 sets being collected for both out-patients and in-patients. The data were analyzed using AMOS 4.0. Results : We found the greater the internal customer satisfaction, the greater the out-patient quality of service quality. Secondly, the greater the service quality, the greater the external customer satisfaction of both in- and out-patients. The service quality of doctors, compared to that of the nurses, had a greater effect on external customer satisfaction. Thirdly, the service quality of doctors and nurses affected both internal and external customer satisfactions, which ultimately affected the customer loyalty. Finally the greater the external customer satisfaction, the greater the customer loyalty. Conclusion : This Study confirms the positive relationship among the internal and external customer satisfactions, service quality, and customer loyalty, which proves the doctors quality of service is the primary factor for external satisfaction, and customer loyalty relating to medical services.