Importance: The efficacy of adalimumab biosimilars is similar to that of brand-name adalimumab (Humira, hereinafter originator) in clinical trials. However, limited knowledge about real-world data exists for adalimumab biosimilars. Objective: To assess the outcomes following a mandatory nonmedical switch from adalimumab originator to adalimumab biosimilars in patients with psoriasis. Design, Setting, and Participants: This cohort study assesses the outcomes following a switch from adalimumab originator to an adalimumab biosimilar. Patients in the Biological Treatment in Danish Dermatology (DERMBIO) registry, a Danish nationwide registry of all patients treated with biologics (including biosimilars) for psoriasis since 2007, were assessed for eligibility. All patients who switched from adalimumab originator to an adalimumab biosimilar between November 1, 2018, and May 1, 2019, were included in the adalimumab biosimilar cohort. All patients with a visit between May 1, 2017, and November 1, 2017, treated with adalimumab originator were included in the adalimumab originator cohort. Data were analyzed from June 1, 2020, to October 10, 2021. Exposure: Switch from adalimumab originator to an adalimumab biosimilar. Main Outcomes and Measures: The primary outcome was 1-year drug retention in patients switching to adalimumab biosimilars compared with patients treated with adalimumab originator. Crude and adjusted retention rates for the adalimumab biosimilar cohort were compared with the adalimumab originator cohort with Cox proportional hazards regression using robust variance. Results: A total of 348 patients were included in the adalimumab biosimilar cohort (mean [SD] age, 52.2 [13.6] years; 251 [72.1%] male) and 378 patients in the adalimumab originator cohort (mean [SD] age, 51.1 [14.1] years; 272 [72.0%] male). The 1-year drug retention rates were 92.0% (95% CI, 89.0%-94.9%) for the adalimumab biosimilar cohort and 92.1% (95% CI, 89.4%-94.8%) for the adalimumab originator cohort. Similar hazard ratios were observed between the 2 cohorts. The crude hazard ratios were 1.02 (95% CI, 0.61-1.70; P =.94) for all causes of drug discontinuation, 0.82 (95% CI, 0.39-1.73; P =.60) for insufficient effect, and 1.41 (95% CI, 0.52-3.77; P =.50) for adverse events for the adalimumab biosimilar cohort when compared with the adalimumab originator cohort. Conclusions and Relevance: In this cohort study from Denmark, a nonmedical switch from adalimumab originator to adalimumab biosimilars was not associated with drug retention..