Psoriasis is a chronic Th-1 and Th-17 inflammatory disease. Chronic inflammation has also been associated with atherosclerosis and thrombosis. The purpose of this study was to determine the risk of stroke in patients with psoriasis. We conducted a population-based cohort study of patients seen by general practitioners participating in the General Practice Research Database in the United Kingdom, 1987-2002. Mild psoriasis was defined as any patient with a diagnostic code of psoriasis, but no history of systemic therapy. Severe psoriasis was defined as any patient with a diagnostic code of psoriasis and a history of systemic therapy consistent with severe psoriasis. The unexposed (control) population was composed of patients with no history of a psoriasis diagnostic code. When adjusting for major risk factors for stroke, both mild (hazard ratio (HR) 1.06, 95% confidence interval (CI) 1.0-1.1) and severe (1.43, 95% CI 1.1-1.9) psoriasis were independent risk factors for stroke. The excess risk of stroke attributable to psoriasis in patients with mild and severe disease was 1 in 4,115 per year and 1 in 530 per year, respectively. Patients with psoriasis, particularly if severe, have an increased risk of stroke that is not explained by major stroke risk factors identified in routine medical care.