Background: Psoriasis is a chronic skin disease associated with lower quality of life and higher risk of anxiety and depression in adults. We investigate whether adolescents with psoriasis also experience poorer mental health than their peers. Methods: In this cross-sectional study, we included questionnaire data on psoriasis and mental health from the 18-year follow-up of the Danish National Birth Cohort. We estimated odds ratios (OR) and 95 % confidence intervals (CI) using a logistic regression with inverse probability weighting to account for potential selection bias, adjusted for potential confounders identified a priori. We estimated associations between self-reported psoriasis and multiple aspects of mental health (self-rated health, life satisfaction, mental well-being, loneliness, overall and internalizing behavioral difficulties, depressive symptoms, and anxiety symptoms). In sensitivity analyses, we examined doctor-diagnosed psoriasis and psoriasis with and without joint pain. Results: Of the 44,838 included in this study, 1147 (2.6 %) reported psoriasis. Adolescents with psoriasis had a higher risk of nearly all outcomes, including depressive symptoms (OR 1.38; 1.19–1.58) and panic/agoraphobia among both males (OR 1.72; 1.33–2.19) and females (OR 1.60; 1.33–1.92). Associations attenuated when restricted to doctor-diagnosed psoriasis. Associations with poor mental health were mainly observed for adolescents with psoriasis also reporting joint pain. Limitations: We could not establish temporality and lacked data on joint pain in referents. Conclusion: Psoriasis is associated with poor mental health in adolescents. This appears to be driven by adolescents with psoriasis also reporting joint pain and is less evident in those with a doctor-confirmed diagnosis.