Importance: Psoriasis is a risk factor for depression. Depression may also trigger or exacerbate psoriasis. The relationship between psoriasis and depression, however, remains to be fully explored., Objective: To investigate the association between psoriasis and major depression in the US population., Design, Setting, and Participants: Population-based study using participants in the National Health and Nutrition Examination Survey from 2009 through 2012., Main Outcomes and Measures: Diagnosis of major depression based on the Patient Health Questionnaire-9., Results: We identified 351 (2.8%) cases of psoriasis and 968 (7.8%) cases of major depression among 12,382 US citizens included in our study. Fifty-eight (16.5%) patients with psoriasis met criteria for a diagnosis of major depression. The mean (SD) Patient Health Questionnaire-9 score was significantly higher among patients with a history of psoriasis than those without psoriasis (4.54 [5.7] vs 3.22 [4.3], P < .001). Psoriasis was significantly associated with major depression, even after adjustment for sex, age, race, body mass index, physical activity, smoking history, alcohol use, history of myocardial infarction (MI), history of stroke, and history of diabetes mellitus (OR, 2.09 [95% CI, 1.41-3.11], P < .001). Interaction term analyses involving patients with a history of both psoriasis and a cardiovascular event, specifically MI or stroke, did not reveal a synergistically increased risk of major depression (psoriasis and MI: OR, 1.09 [95% CI, 0.28-3.60], P = .91; psoriasis and stroke: OR, 0.67 [95% CI, 0.12-3.66], P = .63). In adjusted multivariable models, the risk of major depression was not significantly different between patients with limited vs extensive psoriasis (OR, 0.66 [95% CI, 0.18-2.44], P = .53)., Conclusions and Relevance: Self-reported history of psoriasis was independently associated with major depression as assessed by a validated screening tool, even when controlling for comorbidities. History of cardiovascular event did not modify the risk of major depression for patients with psoriasis. The severity of psoriasis was unrelated to the risk of major depression. Therefore, all patients with psoriasis, regardless of severity, may be at risk for major depression.