To describe an implementation of one information technology system (electronic medical record, EMR) in one hospital, the perceived impact, the factors thought to help and hinder implementation and the success of the system and compare this with theories of effective IT implementation. To draw on previous research, empirical data from this study is used to develop IT implementation theory. Qualitative case study, replicating the methods and questions of a previously published USA EMR implementation study using semi-structured interviews and documentation. Large Swedish teaching hospital shortly after a merger of two hospital sites. Thirty senior clinicians, managers, project team members, doctors and nurses. The Swedish implementation was achieved within a year and for under half the budget, with a generally popular EMR which was thought to save time and improve the quality of patient care. Evidence from this study and findings from the more problematic USA implementation case suggests that key factors for cost effective implementation and operation were features of the system itself, the implementation process and the conditions under which the implementation was carried out. There is empirical support for the IT implementation theory developed in this study, which provides a sound basis for future research and successful implementation. Successful implementation of an EMR is likely with an intuitive system, requiring little training, already well developed for clinical work but allowing flexibility for development, where clinicians are involved in selection and in modification for their department needs and where a realistic timetable is made using an assessment of the change-capability of the organization. Once a system decision is made, the implementation should be driven by top and departmental leaders assisted by competent project teams involving information technology specialists and users. Corrections for unforeseen eventualities will be needed, especially with less developed systems, requiring regular reviews of progress and modifications to systems and timetables to respond to user needs.