Pruritus is the primary symptom of atopic dermatitis (AD). The objective of this study was to develop a patient-reported outcome (PRO) instrument for daily administration in clinical trials to measure AD-related itch in adolescents and adults that would meet the standards described in the US Food and Drug Administration's (FDA's) PRO Guidance. Six focus groups were conducted with 49 patients with AD (32 adults; 17 adolescents). Three iterative rounds of cognitive debriefing interviews were conducted in 26 patients with AD (17 adults; 9 adolescents) to pretest and refine the instrument. AD-related itching was considered the most bothersome AD symptom by nearly two-thirds of the focus group participants. The items in the initial version of the instrument, named the Atopic Dermatitis Itch Scale (ADIS), were developed to reflect concepts most relevant to the assessment of itching as described during the focus groups. Based on results of the cognitive debriefing interviews, an 8-item final version of the ADIS was created. The ADIS is a content valid PRO instrument addressing the concepts critical to the measurement of AD-related itching. To our knowledge, it is the first instrument developed to assess AD-related itch in patients as young as 12 years following the recommendations of the PRO Guidance.