To estimate the cost of illness in adult patients with moderate-to-severe atopic dermatitis (AD) a cohort study was conducted identifying Danish citizens (≥ 18 years) diagnosed with AD between 1997 and 2018 in the Danish National Patient Register. Moderate-to-severe AD was defined as ≥3 hospital contacts regarding AD the first year after  diagnosis. Each patient with AD was matched to 3 reference individuals through the Central Person Registry. Societal costs included the direct costs for primary-sector visits, inpatient hospitalizations, outpatient contacts, prescription medicine and indirect costs of lost productivity 3 years before and 5 years after the index date (the study period). A total of 5,245 patients with moderate-to-severe AD were identified. The mean attributable healthcare costs for patients with moderate-to-severe AD were EUR 10,835 (p < 0.0001) during the study period. Moderate-to-severe AD among adults inferred substantial economic burden compared with a group of matched reference individuals.