Background Inflammation of systemic and vascular tissues besides the skin in psoriasis is associated with cardiovascular morbidity and mortality. Objective We sought to investigate whether or not patients with psoriasis have an increased risk of aortic aneurysm (AA). Methods This population-based cohort study identified 34,301 patients with psoriasis in the Taiwan National Health Insurance Research Database during 2004 to 2006, who were matched for age and sex with 137,204 control subjects without psoriasis from the Taiwan Longitudinal Health Insurance Database 2000. Each individual was individually followed up for 5 years to identify those who subsequently developed AA. Results After adjusting for medical history and medication use, patients with psoriasis were at increased overall risk of AA (adjusted hazard ratio [HR] 1.80; 95% confidence interval 1.25-2.61). The risk for AA increased with the severity of psoriasis. The adjusted HRs were higher for male than female patients (adjusted HR 1.84 vs 1.56), and for patients younger than 50 years versus older patients (adjusted HR 2.81 vs 1.64). Limitations There is a lack of information regarding patients' Psoriasis Area and Severity Index score, daily tobacco use, or alcohol consumption. Conclusion Patients with psoriasis are predisposed to developing AA: this risk increases with psoriasis severity and is independent of established cardiovascular risk factors.