Background: Outsourcing is considered as one of the tools for organizational development and promotion of productivity by managers. In recent years, outsourcing of healthcare services has become significant. The aim of this study was to identify the most important factors influencing the decision making of outsourcing healthcare services. Methods: This study is a combined study. First, the literature was examined to identify the factors influencing decision making for outsourcing. Then, with the aim of consensus on the most important factors affecting the decision making of outsourcing in health services, the panel of experts and Delphi technique were used. Sampling was purposeful. Results: In the selected articles, a total of 180 factors were extracted. The members of the panel of experts from these 180 factors selected 29 sub-factors in the form of six main factors: strategy, quality, management, technology, performance feature, and economy, as the most important factors affecting the outsourcing of services. Finally, the results of Delphi showed that 22 sub-factors were more important in outsourcing decision making at healthcare services. Conclusion: The study showed that the decision making to outsource health services is a complex and multi-criteria decision. Therefore, when deciding to outsource healthcare services, attention should be paid to various factors, such as strategy, quality, management, technology, and economics.