The Young-HUNT Study is the adolescent part of the Trøndelag Health Study (The HUNT Study), a population-based health study inviting all inhabitants, aged 13 years and above, of primarily the northern part of Trøndelag County (former Nord-Trøndelag) in the central part of Norway. The HUNT study has collected data in four subsequent surveys every 11th year from 1984 to 2017, but collections of adolescent data, aged 13 to 19 years, started for the first time in 1995. Young-HUNT1 to Young-HUNT2 cohort, a 4-year follow-up, included 2,399 participants followed from early adolescence (mean age was 13.9 years) to late adolescence. The Young-HUNT1 to HUNT3 cohort was an 11-year follow-up from adolescence (mean age was 15.9 years) to young adulthood. The Young-HUNT allows longitudinal follow-up into adulthood, as well as linkage to a wide range of regional and national health registries by means of the unique identification number allocated to all Norwegian residents.