This paper addresses the problem of emergency surgery insertion into a given elective surgery schedule of an operating theater (OT) composed of multiple operating rooms (ORs). Emergency surgeries with different emergency levels characterized by waiting time targets arrive according to a non-homogeneous Poisson process and can be inserted into any OR. An event-based stochastic programming model is proposed to minimize the total cost incurred by exceeding waiting time targets of emergency surgeries, elective surgery delay and surgery team overtime. A perfect information-based lower bound is proposed and properties of the optimal policies proved. Simple heuristic policies and a stochastic optimization approach derived from the simple policies by policy improvement are proposed. Numerical experiments show that the stochastic optimization significantly outperforms the others and efficient emergency insertion significantly improves the system performance. A principal component analysis is performed to show how near-optimal policies differ from simple heuristic policies. Note to practitioners The paper is motivated by enhancing the efficiency of operating theaters by sharing surgery capacity between elective and emergency surgeries. More specifically , we consider the problem of inserting non-elective surgeries of different * ‡ X. Xie is also with Shanghai Jiao Tong University, Shanghai, China. § Manuscript received month day, year; revised month day, year. 1 emergency levels in the execution of a given elective surgery schedule. A stochas-tic optimization approach is proposed to dynamically prioritize emergency and elective surgeries in order to best balance meeting emergency surgery requirement , perturbation of elective schedule and surgery team overtime. Numerical experiments based on data collected from Saint-Joseph Hospital in Paris show the significant benefit of efficient emergency insertion over the current hospital practice. Elective surgery schedule is shown to have the most important impact on the system performance but efficient emergency insertion always adds significant improvement.