Objective: To evaluate the impact of psoriasis (PsO) on health care utilization and average costs in the first year after diagnosis. Methods: A retrospective study of the PharMetrics database, compiled from managed care plans throughout the United States, from January 1, 2000 through December 31, 2006 was conducted. Patients between the ages of 18 to 80 years, who had a minimum of 12 months of continuous enrollment before and after their initial diagnosis with PsO, were included. The index diagnosis date was derived from the first claim for PsO during the study period. Results: The study cohort included 48,068 patients; 52.3% were female, and the mean age was 46.3 years. Compared with one year prior to the diagnosis, the average cost of treating patients in the year after the diagnosis of PsO was 33% greater (p<0.0001). Post-diagnosis utilizations increased by 2.77 physician visits (mean of 8.44 to 11.21), 1.92 prescriptions (mean of 9.56 to 11.48), 0.34 outpatient visit (mean of 1.39 to 1.73), 0.22 laboratory service (mean of 0.94 to 1.16), 0.02 inpatient stay (mean of 0.13 to 0.15), and 0.02 emergency room visit (mean of 0.18 to 0.20). Also, the inpatient length of stay increased by 0.34 day (mean of 1.39 to 1.73). All changes were statically significant with Wilcoxon Signed-Rank Tests (p<0.001). Conclusion: This study indicates that following a diagnosis of PsO, health care utilization and average costs in the first year after such a diagnosis increases significantly. While we found that the greatest increase occurred in the number of physician office visits, additional studies are needed to further explore the reasons for the large increase (33%) in the cost of treating patients in the first year after a diagnosis of PsO.