INTRODUCTION: Lolland-Falster consists of two islands in the southern part of Denmark where income is lower and life expectancy is shorter than in the general Danish population. It is a mixed rural-provincial area with approximately 100,000 inhabitants. The Lolland-Falster Health Study was initiated to gain knowledge on the determinants of health in this disadvantaged area.

METHODS: The study is a household-based prospective cohort study including people of all ages. The entire household of randomly selected inhabitants is allocated either to an invited group or to an uninvited, non-contacted control group. The data collection encompasses questionnaires, physical examination and biological samples, i.e. blood and urine for same-day analysis and biobank storage, and saliva and faeces also for biobank storage. The civil registration number links collected data for each individual, family and household, with information in Danish registers. The data collection started in February 2016 and is estimated to end by 2019 after the enrolment of 20,000 people.

ANALYSIS: A number of in-depth sub-studies are planned. Emphasis will be given to analysis of intra- and inter-family variations in health determinants, genetics, lifestyle and health status. Ethics: Region Zealand's Ethical Committee on Health Research (SJ-421) and the Danish Data Protection Agency (REG-24-2015) approved the study.

TRIAL REGISTRATION: Clinicaltrials.gov (NCT02482896). Strength and limitations of this study: The strength of this study is that Lolland-Falster Health Study is a useful scientific resource for investigating cross-sectional difference and time trends within and between individuals, families and households. LOFUS adds diversity to the previously collected Danish population studies in urbanized areas. The limitation is that data collection is expensive.

CONCLUSIONS: LOFUS will contribute to the knowledge on health in disadvantaged, rural-provincial areas.