Introduction: The impact of asthma and disease control on job absenteeism in young adults is sparsely investigated and conflicting evidence exist. Based on a nationwide cohort, the present study aims to describe the overall job absenteeism across asthma severities and describe the possible influence of asthma control. Methods: REASSESS is a nationwide cohort of Danish asthma patients aged 18–45 using controller medication between 2014 and 2018, followed retrospectively for up to 15 years using national databases. Impact of asthma was investigated using negative binomial regression adjusted for age, sex, Charlson score and level of education and presented as adjusted incidence rate ratios with 95% confidence intervals. Results: A total of 60,534 patients with asthma (median age 33 (25, 39), 55% female, 19% uncontrolled disease and 5.7% possible severe asthma) were followed for 12.7 (6.5–14.8) years. The prevalence of any absenteeism was more common in both mild-to-moderate and possible severe asthma compared to the background population (67%, 80% and 62%, respectively; p < 0.0001). Compared to the background population, mild-to-moderate and possible severe asthma were more likely to have temporary sick leave (1.37 (1.33–1.42); 1.78 (1.62–1.96)), unemployment (1.11 (1.07–1.14); 1.26 (1.15–1.38)) and obtain disability benefits (1.67 (1.66–1.67); 2.64 (2.63–2.65)). Uncontrolled asthma had increased temporary sick leave (1.42 (1.34–1.50)), unemployment (1.40 (1.32–1.48)) and disability (1.26 (1.26– 1.27)) when compared to controlled disease. Significant increases in absenteeism could be measured already at ≥100 annual doses of rescue medication (1.09 (1.04–0.1.14)), patients’ first moderate or severe exacerbation (1.31 (1.15–1.49) and 1.31 (1.24–1.39), respectively). Further increases in absenteeism were observed with increasing rescue medication use and severe exacerbations. Conclusion: Across severities, job absenteeism is increased among patients with asthma compared to the background population. Increases in absenteeism was seen already at ≥100 annual doses of rescue medication, representing a substantial, and probably preventable, reduction in productivity among young adults.