Introduction: The Length of Stay (LOS) in the hospital is used as an indirect indicator of resources consumption and efficiency in hospitals. Identifying factors associated with this systematic review can be valuable in planning to optimize the utilization of the existing resources. The goal of the present study was to investigate factors associated with length of stay and it has been conducted as a systematic review.
Method: In this systematic review, papers were retrieved by the use of specified key terms in their titles and no restricted time in Persian and English databases. Papers were selected according to how they were in line with the criteria for inclusion and exclusion and finally, information were extracted and entered to Excel 2010 software for analysis.
 Results: 18 articles out of 347 were selected. These studies introduced four criteria associated with length of stay including clinical, demographic, administrative, and hospital factors. Applied methods for identifying these criteria were statistical techniques and data mining techniques such as decision tree regression and artificial neural networks. The goal of all studies was making a new model for identifying factors associated with LOS or was evaluating other methods introduced in other studies.
Conclusion: Findings of this study represent that identifying factors associated with LOS can be variable according to data collection place, studied variables, and applied data mining techniques. So we suggest researchers to help hospital managers and planners with identifying and reducing factors associated with LOS.