Abstract Background Recent findings in psoriasis research have shown that psoriasis is frequently associated with systemic comorbidities. Objectives This study aims to describe the epidemiology of psoriasis and the prevalence of comorbidities in patients with psoriasis in Taiwan. Methods Patients who had at least one outpatient visit or admission with ICD-9-CM diagnosis code 696.0-1 in the Taiwan National Health Insurance (NHI) claims database during 2006 were identified as psoriasis cases. The cases were further classified into moderate to severe psoriasis (sPsO) for those who had previously received systemic therapy during the study period and mild psoriasis (mPsO) for those who had not. The cases were matched in a 1:4 ratio with controls from a sample cohort of 997,771 enrolees representative of the Taiwan population. Matching variables included age, gender and residential area. Prevalence of comorbidities was assessed using prevalence relative risk (RR) based upon a Cox proportional regression model. Results 51,800 psoriasis cases were identified (prevalence = 0.235%; mean age = 46.4 ± 18.6; male:female = 1.6:1) and 17.5% of cases were sPsO type. Psoriasis was associated with a significantly increased prevalence ratio (RR; 95% confidence interval) for hypertension (1.51; 1.47, 1.56), diabetes (1.64; 1.58, 1.70), hyperglyceridaemia (1.61; 1.54, 1.68), heart disease (1.32; 1.26, 1.37), hepatitis B viral infection (1.73; 1.47, 2.04), hepatitis C viral infection (2.02; 1.67, 2.44), rheumatoid arthritis (3.02; 2.68, 3.41), systemic lupus erythematosus (6.16; 4.70, 8.09), vitiligo (5.94; 3.79, 9.31), pemphigoid (14.75; 5.00, 43.50), pemphigus (41.81; 12.41, 140.90), alopecia areata (4.71; 2.98, 7.45), lip, oral cavity and pharynx cancer (1.49; 1.22, 1.80), digestive organs and peritoneum cancer (1.57; 1.41, 1.74), depression (1.50; 1.39, 1.61), fatty liver (2.27; 1.90, 2.71), chronic airways obstruction (1.47; 1.34, 1.61), sleep disorder (3.89; 2.26, 6.71), asthma (1.29; 1.18, 1.40), and allergic rhinitis (1.25; 1.18, 1.33). Conversely, psoriasis was not associated with an increased risk of Crohn's disease. Conclusions Psoriasis was associated with a significantly increased risk of comorbidities, especially for those patients with moderate to severe disease. These health associations should be taken into consideration when evaluating the burdens of psoriasis and designing effective treatment plans.