An interdisciplinary research group entitled "Twincities Research Group" has been initiated at Linkoping University. The term twin cities refer to the Swedish cities Linkoping and Norrkoping, neighbors that are nearly equal in size. These two cities, located within a distance of only 40 km, are governed by the same county council and consequently have the same health care structure. However, public health is remarkably different in these twin cities. The comparison of public health in these two cities during the development from the industrial to the post-industrial era has a design similar to classical experiments with a control and an experiment group, since the social history and the socio-economic structures of the cities are radically different. Through an interdisciplinary research design including historical, epidemiological and clinical competence we have a unique opportunity to increase our understanding of how the social environment may affect public health.