OBJECTIVE: The impact of psoriasis medication therapy on costs and patient outcomes in large nationally representative samples needs further examination. The study examined the association between factors related to medication use and costs linked with the treatment of psoriasis in the United States. METHODS: Longitudinal cohort study using the United States Medical Expenditure Panel Survey (MEPS) Database (1996-2001). Information on health care service utilization, costs, demographics and clinical patient variables were obtained from the MEPS dataset. Self-reported health status information was obtained from the EuroQoL (EQ-5D) used in MEPS. Multivariate weighted analysis was performed on data for approximately 333,000 patients (weighted sample size). RESULTS: Approximately 44% of the psoriasis-specific health care cost in patients was accounted by medications alone, with an average of 3.4 psoriasis prescription refills annually. Topical corticosteroids were used by as many as 57.1% of patients, 30.5% used other medications, while, 12.4% did not receive any pharmacological treatment. About 42% of the variance was explained by the multivariate models examining predictors of health care costs. Among medication-related factors, increased psoriasis prescription refill rates were associated with an increase in psoriasis-specific health care costs (p=0.009). Increase in frequency of office-based visits was the primary driver of increased psoriasis-specific health care costs (p=0.02). There were no significant differences in health care costs among patients using different types of psoriasis medications. CONCLUSIONS: Cost towards psoriasis medications account for most of the psoriasis-specific health care costs. Increase in frequency of office-based visits seems to be the primary driver of increased psoriasis-specific health care costs.