During the last years, and due to social and economic changes, the demand for private health services (PHS) is growing. A more significant number of companies appeared under different business model formulas. Besides the traditionally independent professionals, other types of entrepreneurs appeared under associated business. As a result of these changes, there are differences in how these services are provided and their performance. OBJECTIVES: This work is proposed to study the business model effect on small private health service companies' activity and analyze institutions’ and intellectual capital's role in their performance. METHODOLOGY: A qualitative-quantitative mixed method was designed. The qualitative design allows knowing in depth the professionals' opinions related to the competitive scenario, the perception of knowledge, and how it is acquired and managed. For quantitative research, we asked about the intellectual capital they have, the institutions' role, and the assessment of their competitiveness. The hypotheses were checked using Qualitative Comparative Analysis, non-parametric techniques combined with a qualitative study. RESULTS: The phenomenon of associated business models (ABM) promotes synergies in scale economies, branding sharing, cost savings, or more effective knowledge transfer. Although these ABMs are not directly associated with better performance, the actions mentioned above are associated with better results. CONTRIBUTIONS: Academically, this thesis contributes to Knowledge-Intensive Based Services (KIBS) literature. More specifically, PHS belong to professional KIBS. Socially, the results illustrate some problems that the different institutions related to these services have to face. At the professional level, this work includes some findings for improving the performance of these companies.