A number of controlled healthcare terminologies and classification systems have been developed for specific purposes, resulting in variations in content, structure, process management, and quality. A terminology quality improvement (TQI) model or framework would be useful for various stakeholders to guide terminology selection, to assess the quality of healthcare terminologies and to make improvements according to an agreed standard. A TQI model, thus, was formulated based on a review of the literature and existing international standards developed for healthcare terminologies. The TQI model, adapted from Donabedian’s approach, encompasses structure, process, and outcome components in relation to a terminology life cycle – change request, editing, and publication. Multi-dimensional quality outcome measures also were identified in the areas of terminology content, modeling structure, mapping, and process management. A case study was developed to validate the TQI model using the International Classification for Nursing Practice (ICNP). The TQI model represented the complexity of activities involved in terminology quality management. The ICNP case study demonstrated both the applicability of the TQI model and the appropriateness of the criteria identified in the TQI model: openness and responsiveness, clarity and reproducibility, understandability, accessibility and usability, interoperability, and quality of documentation. The applicability of the TQI model was validated using ICNP. While ICNP exhibits many of the desirable characteristics of contemporary terminologies, the case study identified a need for further work on ICNP policy and on documentation.