OBJECTIVES: Psoriasis is a chronic immune-mediated inflammatory disorder and is associated with concurrence of other complex disorders. This study aims to describe the epidemiology of psoriasis and the prevalence of co-morbidities in patients with psoriasis in Taiwan. METHODS: Patients who had at least one outpatient visit or admission diagnosed with ICD-9-CM 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 and mild psoriasis (mPsO) for those who had not. The cases were matched with controls in a 1:4 ratio from one million beneficiaries in the NHI dataset representing the Taiwan population.  Matching variables included age, gender and residential area. Prevalence of co-morbidities was assessed using prevalence relative risk (RR) based upon a Cox proportional regression model. RESULTS: The prevalence of psoriasis in the overall population was 2.35‰ (n=53,761). Mean age (SD) was 46.2 (±18.6) and 60% were male.  Of the 53,761 psoriasis cases, 17.2% (n=9,265) were the sPsO type. sPsO patients had a significantly increased prevalence ratio (RR; [95% confidence interval ])for hypertension (1.33; [1.26, 1.40]), diabetes (1.52; [1.42, 1.63]), hyperglyceridaemia (1.56; [1.44, 1.69]), heart disease (1.24; [1.14, 1.34]), depression (1.44; [1.23, 1.69]), hepatitis B (1.95; [1.44, 2.65]) and hepatitis C (2.19; [1.49, 3.22]). Increased risk of these comorbidities was also observed in mPsO patients compared to controls, but with a smaller magnitude compared to sPsO. CONCLUSIONS: Psoriasis was associated with a significantly increased risk of co-morbidities, especially for those patients with moderate to severe disease. These health consequences should be taken into consideration when evaluating the burdens of psoriasis and designing effective treatment plans.