OBJECTIVES: To estimate the financial impact of adopting ustekinumab as an additional psoriasis treatment option on a United States (US) health plan formulary, while incorporating comparative evidence. METHODS: The model perspective was a 1 million-member US health plan (including only direct healthcare costs).  Psoriasis prevalence and biologic penetration rates were derived from publically available US sources. Base case analysis examined increasing ustekinumab market share from launch through 5 years, with commensurate decreases in market share of other biologics.  Treatment costs (adalimumab, etanercept, infliximab, and ustekinumab) were computed using August 2011 wholesale acquisition costs and US FDA prescribing information for induction/maintenance dosing.   Responder and non-responder cohorts were modeled based on disease response rates. Responder cost inputs included drug acquisition/administration/monitoring/outpatient visits. Non-responder cost inputs included supportive care/inpatient costs. No clinically significant differences in rates of adverse events requiring treatment were assumed. RESULTS: In each modeled year, 0.03% of the health plan population would receive biologic treatment for moderate to severe psoriasis. Without ustekinumab, total biologic drug budget in the base year was predicted to be $8.42 million, and total annual medical budget for moderate to severe psoriasis was estimated at $9.80 million. By year 5, estimates increased by 4.7%. By adding ustekinumab, estimated therapy budget increased by 6.3% and overall medical budget increased by 3.7% over the course of 5 years.  These estimates incorporated comparative data, which predicted the number of disease responders increasing by 15% over the same period.  Net budget increase for all covered lives was estimated at $0.031 per member per month by year 5. CONCLUSIONS: Model results indicated reimbursement for ustekinumab may have minimal impact on a US health plan’s budget, given the relatively small size of the eligible population.  Additionally, by including comparative evidence, results illustrated the estimated positive clinical impact of adding ustekinumab to formulary.