Introduction: Nemolizumab, a new monoclonal antibody that targets the receptor alpha of the neuroimmune cytokine interleukin-31 (IL-31), has shown efficacy in atopic dermatitis (AD) in adults. This study evaluated the pharmacokinetics (PK) and safety of nemolizumab in adolescents with moderate to severe AD as well as the relationship between nemolizumab concentrations and clinical efficacy and the effect of nemolizumab on protein biomarkers. Methods: Open-label, 16-week study of nemolizumab in patients aged 12-17 years with moderate to severe AD (baseline EASI C 16, IGA C 3, and BSA C 10%) and associated pruritus with baseline average daily peak pruritus numeric rating scale (PP-NRS) intensity of at least 4. Nemolizumab was administered subcutaneously as a loading dose of 60 mg at baseline, followed by 30 mg every 4 weeks until week 12 with background topical corticosteroids (TCS) or calcineurin inhibitors (TCI). Subsequently patients were followed for 8 weeks more. Stratum corneum (SC) and plasma samples were collected for biomarker assessments. Results: Twenty patients participated, with a mean age of 14.8 ± 1.6 years. The PK of nemolizumab was described by a one-compartment model with linear elimination, a first-order absorption, and a mean half-life of 16.7 ± 4.1 days. Mean trough concentrations ranged from 2935 ± 1029 ng/mL to 3292 ± 2018 ng/mL over the 16-week treatment period.