The Koster Islands are the westernmost inhabited islands of Sweden, located in the Skagerrak, close to the Norwegian border, some 10 km west of the mainland town of Stromstad. The islands have had a permanent population since the fourteenth century. By tradition, the islanders demonstrate very little geographic mobility, which makes it possible to study several generations of the same family from Koster. No specific genetic disorders exist.
Population growth is positive and young people prefer to go on living on the islands.
The main industries are fishing and the tourist trade. There are very few cars on Koster, the commonest means of transportation being motorbike and bicycle. This makes for very little motor traffic. Moreover, the area has no polluting industries. Thus, the Koster islands provide a unique possibility for studying changes in the background environment of western Sweden.