Psoriasis increases the risk of atrial fibrillation (AF) and thromboembolic events (TE). There is limited information on the effect of psoriasis severity on AF and TE. In this study, psoriasis patients were enrolled from the Korean National Insurance Service-National Sample Cohort (2004-2008). Diagnosis and disease severity were determined from claims data. Newly diagnosed non-valvular AF and TE were identified during a 9.6-year follow-up. The effect of psoriasis severity on AF and TE was evaluated. We identified 13,385 psoriasis patients (1,947 with severe psoriasis). Severe psoriasis significantly increased the risk of AF (adjusted hazard ratio [HR_adjust] 1.44 [95% confidence interval (CI) 1.14-1.82], p = 0.002) and TE (HR_adjust 1.26 [95% CI 1.07-1.47], p = 0.005); mild psoriasis did not show any significant effects. Results were similar after propensity-score matching. Risk increments of AF and TE were prominent in patients with greater cardiovascular risk. A possible limitation of our study is that it has a retrospective design, and the effect of unmeasured confounders and risk of misclassification could bias the results. To conclude, our results showed that severe, but not mild, psoriasis significantly increased AF and TE risk. AF surveillance and active stroke prevention would be beneficial in such cases.