Background: No age-appropriate and disease-specific instrument currently exists to measure health-related quality of life in adolescents with psoriasis (patients aged 12–17 years). Objectives: To develop and provide preliminary validation of the Adolescent Psoriasis Quality of Life instrument. Methods: Qualitative interviews with adolescents with psoriasis, parents of adolescents with psoriasis, and healthcare professionals informed the development of an initial item pool for the instrument, which was subsequently refined through cognitive interviews. Finally, data from an independent sample of adolescents with psoriasis (n = 50) were used for item reduction, scale construction and initial validation, using a combination of techniques from classical test theory and Rasch modelling. Results: Rich qualitative data concerning health-related quality of life in adolescents with psoriasis (from 18 adolescents, 14 parents and four healthcare professionals), combined with cognitive interview testing (n = 12), resulted in a 41-item draft version. Item reduction led to the final version, a 17-item instrument consisting of two subscales showing good fit to their respective Rasch models: psychosocial impact (12 items) and the impact of physical symptoms and treatment (five items). All a priori stated hypotheses regarding construct validity were supported. Both subscales and the total scale showed acceptable test–retest reliabilities (intraclass correlations 0·97, 0·89 and 0·96) and internal consistencies (Cronbach's α 0·94, 0·81 and 0·95). Conclusions: The preliminary form of the Adolescent Psoriasis Quality of Life instrument shows promising psychometric properties. It can be used in daily clinical practice and research to support a patient-centred approach and inform treatment planning. What's already known about this topic?. Health-related quality of life (HRQoL) instruments should be targeted towards narrowly defined age groups, as life contexts of children, adolescents and adults may differ substantially. Dermatology-specific instruments have been used to measure HRQoL in adolescents with psoriasis, but it is not known whether these instruments accurately capture all relevant HRQoL aspects in adolescent psoriasis. Age-appropriate and psoriasis-specific instruments may be more sensitive for HRQoL issues experienced by this unique group. What does this study add?. The Adolescent Psoriasis Quality of Life instrument represents the first age-appropriate and disease-specific instrument for measuring HRQoL in adolescents (12–17 years old) with psoriasis. It is intended for use in daily clinical practice to support dermatologists and other healthcare professionals in providing optimal care for adolescents with psoriasis.