Since 2011, 15 Danish municipalities have implemented smoke free work hours, meaning that an employee working for the municipality may not smoke in his or her work time (about 7,5 hours a day). This is a much stricter prevention method, than former strategies preventing smoking mostly at locations and not during working hours. Research concerning the effects of smoke free work hours is non-existing. We therefore wish to look into the specific outcomes of smoke free work hours related to smoking prevalence, sickness leave and work place culture through a semi-experimental study. As the decision to implement smoke free work hours is administrative and/or political, we will not be able to randomize the intervention. Instead, we use one or more Danish municipality who are planning to implement smoke free work hours as an intervention-group and similar municipalities as control group. Data will be collected both through questionnaires about employees smoking prevalence, sickness leave and work place community, and through register data about the citizens employed in the municipalities in question. This will primarily be data on socio-economic status and health. In this way we can compare the municipalities implementing smoke free work hours with each other and find similar control municipalities. We hope, that this study can contribute to understanding the specific outcomes of implementing smoke free work hours, focusing both on health outcomes and work place culture.