Atopic dermatitis (AD; also known as atopic eczema) is an inflammatory skin disease. The safety and effectiveness of upadacitinib for AD has been well-documented in previous studies, however, these studies included a limited number of adolescent patients in Japan. Therefore, the purpose of this observational study is to evaluate safety and effectiveness of upadacitinib in adolescent AD participants age 12 to \<18 years old in Japan in the real-world setting. Upadacitinib is an approved drug being developed for the treatment of AD in adolescents in Japan. Around 170 participants age 12 to \<18 who are prescribed upadacitinib for the treatment of AD in routine clinical practice will be enrolled at multiple sites in Japan. Participants will receive oral upadacitinib as prescribed by their physician. Data from these participants will be collected for approximately 2 years. There will be no additional burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the course of the study at a hospital or clinic and will be asked to provide additional information by questionnaire at each visit.