OBJECTIVES: To evaluate the risk of psychiatric disorders and associated health care expenditures among moderate to severe psoriasis (PsO) patients using data from a US health care claims database. METHODS: PsO patients and controls without PsO were identified from the PharMetrics healthcare claims database using the ICD-9 code of 696.x. Patients with moderate to severe PsO (N=7971) had been diagnosed with PsO in both years 2003 and 2004, and had been treated with systemic therapies including cyclosporine, methotrexate, acitretin, biologics, or phototherapy. Controls (N=31884) were matched with PsO cases in a 4:1 ratio by gender, age, region, and previous time-in-plan. Psychiatric disorders and anti-psychiatric therapies in year 2004 were compared between groups. RESULTS: PsO cases were equally distributed between males (50.6%) and females with mean age of 47.2 years. Almost half of the patients received anti-inflammatory drugs, 33.3% received biologic therapies, and 36.7% had phototherapy. Compared with controls, patients with moderate to severe PsO had a statistically significantly higher prevalence (p<0.01) of anxiety (6.94% vs. 4.37%, OR=1.63), depression (9.17% vs. 5.32%, OR=1.80), bipolar disorder (1.10% vs. 0.51%, OR=2.16), and delirium (0.25% vs. 0.14%, OR=1.74). There was no difference between PsO patients and controls in the prevalence of dementia or schizophrenia (p>0.05). Compared with controls, a greater proportion of PsO patients had been treated with antidepressants (6.12% vs. 0.90%, OR=7.18), anxiolytics (5.03% vs. 0.75%, OR=7.04), anti-psychotics (5.90% vs. 0.89%, OR=6.97) or anti-manics (4.89% vs. 0.74%, OR=6.93). PsO patients had higher total health care expenditures ($11,538.8) than controls ($42,18.7, p<0.0001). Among the PsO patients, those with any psychiatric disorders had a total health care expenditure of $18,046.70, as compared with $10,503.50 for those without psychiatric disorders (p<0.0001). CONCLUSIONS: PsO patients have a significantly higher prevalence of psychiatric disorders as compared with patients without PsO. PsO patients with psychiatric disorders have significantly higher health care expenditure than those without such disorders.