One of the pillars for sound Software Project Management is reliable effort estimation. Therefore it is important to fully identify what are the fundamental factors that affect an effort estimate for a new project and how these factors are inter-related. This paper describes a case study where a Knowledge Management technique was employed to build an expert-based effort estimation model to estimate effort for healthcare software projects. This model was built with the participation of seven project managers, and was validated using data from 22 past finished projects. The model led to numerous changes in process and also in business. The company adapted their existing effort estimation process to be in line with the model that was created, and the use of a mathematically- based model also led to an increase in the number of projects being delegated to this company by other company branches worldwide.