The purpose of this study is to develop a methodology by extending the Technology Acceptance Model (Davis, 1989) in order to contribute the acceptance of Hospital Management Systems in hospitals. The study also aims to extend the TAM by adding external variables. Thereby the relationships between perceived usefulness, perceived ease of use and external TAM factors and how these relationships will affect the behavioral intention to use the technology will be determined. In this study quantitative research methods are used. Quantitative research comprises from a questionnaire which is tested in Turkish government hospitals by hospital personnel, physicians, nurses, technicians and administrative personnel. After collection of data from quantitative research the analysis of the data was conducted. The findings of the analysis gave the significant relationships between perceived usefulness, perceived ease of use, behavioral intention and external variables. In conclusion this study points out the effects and the compatibility of the critical factors of TAM on the user acceptance of Hospital Management Systems in Turkish hospitals.