Health Information Systems (HIS) are being implemented in all aspects of healthcare; from administration to clinical decision support systems. Usability testing is an important aspect of any HIS implementation with much done to deliver highly usable systems. However, evidence shows that having a highly usable system is not enough. Acceptance by the clinician users is critical to ensure that the HIS implemented is used fully and correctly. A longitudinal case study of the implementation of the Community Health Information Management Enterprise System (CHIME) in NSW is used to illustrate the importance of ensuring clinician acceptance of a HIS. A mixed methods approach was used that drew on both qualitative and quantitative research methods. The implementation of CHIME was followed from the early pre-implementation stage to the post implementation stage. The usability of CHIME was tested using expert heuristic evaluation and a usability test with clinician users. Clinician acceptance of CHIME was determined using the Technology Acceptance Model (TAM). The clinician users were drawn from different community health service departments with distinctly different attitudes to information and communication technology (ICT) in healthcare. The results of this research identified that a successful implementation of a HIS is not a measure of its quality, capability and usability, but is influenced by the user's acceptance of the HIS.