This cohort study used prospectively collected data from the Swedish national quality registry, SwedAD, to investigate weight gain as a possible side effect of dupilumab treatment for atopic dermatitis. Patients on dupilumab were compared with patients on other systemic medications, e.g., methotrexate, cyclosporine, or Janus kinase inhibitors, and possible risk factors for weight change during treatment with dupilumab were analysed. All patients aged 18 years or above, included in SwedAD between March 2018 and April 2023, who initiated systemic treatment at or after inclusion and had data on weight at baseline and at least 1 follow-up weight measurement were included (n = 157). After 2 years on dupilumab, patients had a mean weight gain of 1.6 kg (p = 0.007, 95% confidence interval [CI] 0.4-2.7). In the multivariable analysis, controlling for age at start, sex, asthma, and body mass index at start, dupilumab was associated with higher weight gain than other systemic treatments (3.3 kg, p = 0.005 [95% CI 1.0-5.6]). Asthma was associated with weight loss; male sex tended to be associated with weight gain.