Sickness absenteeism among nurses is a major quandary for all health care institutions. It creates an economic burden and impacts patient outcomes. Unfortunately, no study explored the reasons of nurse absenteeism in the Middle East. Hence, the aim of this study is to explore the Nurse Manager perceptions of factors related to absenteeism among nurses in a Tertiary Medical Center in Lebanon. Methods: A qualitative descriptive design was used. Twenty four nurse managers were interviewed. Institutional review board approval was granted prior to data collection. Results: Content analysis yielded to the following domains: individual factors interpersonal factors, job factors, and organizational factors. Conclusion: Sickness absenteeism represents an acute problem in most institutions. Based on the reasons reported by Nurse Managers, emphasis should be placed on the physical, psychological, socio-economic and family factors as well as on education on work ethics, commitment and responsibility. Implications: Healthcare Administrators need to explore nurse absenteeism in order to design a sickness management program to control financial and non financial costs of nurse absenteeism.