Using event study methodology and two-stage regression analysis on a sample of firms announcing human resource outsourcing (HRO) contracts, this study tests the association between administrative HRO and firm-level capital market and long run operating performance, with archival financial data controlling for endogeneity and outsourcing decision optimality. The results demonstrate that the equity capital market responds positively to client firms announcing administrative HRO, particularly service firms and those outsourcing transactional HR tasks. Additional statistical analysis shows that suboptimal outsourcing is negatively associated with long run operating performance measured as return on assets and operating return on assets. This study contributes to outsourcing literature by more precisely quantifying outsourcing performance through archival financial data and employing capital market empirical tests. Further, it controls for outsourcing decision optimality in examining long run operating performance effects. This research focuses on HR, a critical function within the firm and value enhancing to the firm.