Nikoline Lund Jensen,1,2 Henrik Søndergaard Pedersen,1 Mogens Vestergaard,1,2 Stewart W Mercer,3 Charlotte Glümer,4 Anders Prior,1,2 1Research Unit for General Practice, 2Section for General Medical Practice, Department of Public Health, Aarhus University, Aarhus, Denmark; 3General Practice and Primary Care, Institute of Health and Wellbeing, University of Glasgow, Glasgow, Scotland; 4Research Centre for Prevention and Health, The Capital Region of Denmark, Glostrup, Denmark Objective: Multimorbidity (MM) is more prevalent among people of lower socioeconomic status (SES), and both MM and SES are associated with higher mortality rates. However, little is known about the relationship between SES, MM, and mortality. This study investigates the association between educational level and mortality, and to what extent MM modifies this association. Methods: We followed 239,547 individuals invited to participate in the Danish National Health Survey 2010 (mean follow-up time: 3.8 years). MM was assessed by using information on drug prescriptions and diagnoses for 39 long-term conditions. Data on educational level were provided by Statistics Denmark. Date of death was obtained from the Civil Registration System. Information on lifestyle factors and quality of life was collected from the survey. The main outcomes were overall and premature mortality (death before the age of 75). Results: Of a total of 12,480 deaths, 6,607 (9.5%) were of people with low educational level (LEL) and 1,272 (2.3%) were of people with high educational level (HEL). The mortality rate was higher among people with LEL compared with HEL in groups of people with 0–1 disease (hazard ratio: 2.26, 95% confidence interval: 2.00–2.55) and ≥4 diseases (hazard ratio: 1.14, 95% confidence interval: 1.04–1.24), respectively (adjusted model). The absolute number of deaths was six times higher among people with LEL than those with HEL in those with ≥4 diseases. The 1-year cumulative mortality proportions for overall death in those with ≥4 diseases was 5.59% for people with HEL versus 7.27% for people with LEL, and 1-year cumulative mortality proportions for premature death was 2.93% for people with HEL versus 4.04% for people with LEL. Adjusting for potential mediating factors such as lifestyle and quality of life eliminated the statistical association between educational level and mortality in people with MM. Conclusion: Our study suggests that LEL is associated with higher overall and premature mortality and that the association is affected by MM, lifestyle factors, and quality of life. Keywords: multimorbidity, socioeconomic status, social epidemiology, inequality in health, mortality, population-based cohort study