The Northern Swedish Cohort was started by Anne Hammarstrom [principal investigator (PI)] in collaboration with Urban Janlert and other researchers within the field of social medicine (Ragnar Berfenstam, Finn Diderichsen, Tores Theorell, Lars H Gustafsson, Claes Sundelin, Gustav Jonsson). At that time, the PI was a newly qualified registered medical doctor and was searching for a PhD project. An older colleague advised us to start a longitudinal study, which could be the database for our future research. The background to the study was the relatively high unemployment rate among young people in Sweden at the beginning of the 1980s. Whereas some studies were available about the health consequences of unemployment in the adult population, there was a lack of research about possible health consequences of youth unemployment. Thus, we decided to perform a longitudinal study of a cohort of school-leavers. The chosen setting was Northern Sweden, as the highest levels of both youth and adult unemployment were found in that part of Sweden. In fact, unemployment had been endemic in this part of Sweden for a long time. The county capital of Norrbotten, Lulea, was chosen as this is a typical middle-sized, industrial town, which is comparable to Sweden as a whole with regard to important socio-demographic background data such as labour market structure, percentage of foreign born, housing, divorce rate and socio-economic status. Initially, we planned to follow up the cohort after 2 and 5 years. However, after the first 5 years, the study had attracted the interest of the scientific community and of policymakers, and thus there was a request for new follow-ups.