In light of growing demands for public accountability, the broadening scope of health technology assessment organizations (HTAOs) activities and their increasing role in decision-making underscore the importance for them to demonstrate their performance. Based on Parson's social action theory, we propose a conceptual model that includes four functions an organization needs to balance to perform well: (i) goal attainment, (ii) production, (iii) adaptation to the environment, and (iv) culture and values maintenance. From a review of the HTA literature, we identify specific dimensions pertaining to the four functions and show how they relate to performance. We compare our model with evaluations reported in the scientific and gray literature to confirm its capacity to accommodate various evaluation designs, contexts of evaluation, and organizational models and perspectives. Our findings reveal the dimensions of performance most often assessed and other important ones that, hitherto, remain unexplored. The model provides a flexible and theoretically grounded tool to assess the performance of HTAOs.