To determine the current state of knowledge regarding the effects of deployment length and a 'mismatch' between the expected and actual length of deployments on the health and well-being of military personnel in order to draw relevant conclusions for all organisations that deploy personnel to conflict zones. A systematic review was conducted of studies measuring deployment length to theatres of operations and the issue of 'mismatch' between expected and actual tour lengths. The nine studies included were rated for quality. Of the nine studies reviewed, six were rated as high quality, two as moderate quality and one as low quality. Seven of these studies found adverse effects of longer deployments on health and well-being. The two studies that measured 'mismatch' found adverse effects on mental health and well-being when deployments lasted longer than personnel expected. There are a limited number of studies which have assessed the effects of deployment length and very few that have assessed the effects of 'mismatch' on health and well-being. However, this review suggests that, as deployment length increases, the potential for personnel to suffer adverse health effects also increases. Further research is required to investigate the effects of spending prolonged periods of time away from family and friends, especially when deployment lasts longer than expected by personnel. These results are important not only for the Armed Forces, but also for other organisations that place employees in similar working conditions. Taking account of these findings may allow better preparation for the potentially harmful effects that deployments can have on employees' health and well-being.