OBJECTIVES: To estimate annual cost per treated patient for etanercept, adalimumab, infliximab, abatacept, rituximab, golimumab, certolizumab, and ustekinumab in rheumatoid arthritis (RA), psoriasis, psoriatic arthritis, and ankylosing spondylitis in a US claims population. METHODS: MarketScan Commercial Database was used to identify patients (18-63 years) with ≥1 claim for a biologic of interest between January 1, 2008 and December 31, 2010 preceded by ≥6-months of enrollment and a diagnosis of RA, psoriasis, psoriatic arthritis, or ankylosing spondylitis. The first drug claim meeting these criteria defined the index date and biologic. “Continuing” patients had ≥1 claim for the same biologic before their index date, “New” patients did not. Patients were required to be continuously enrolled for 1-year following the index claim. Patients with Crohn’s disease, or ulcerative colitis pre-index were excluded since not all biologics are approved for these indications. Mean monthly dose and total dose of other biologics after discontinuation of their index biologic was calculated for the 12-months after index. Wholesale acquisition costs and the Medicare Physician Fee Schedule were applied to the mean monthly dose and related drug administration to calculate cost per treated patient. RESULTS: A total of 69,349 patients were included, 92.3% received etanercept (32,298), adalimumab (20,582), or infliximab (11,157).  Patient characteristics were similar across groups; mean age 47.8 years (SD 10.2), 63% female. Mean annual cost per treated patient pooled across indications was $20,508 etanercept, $21,179 adalimumab, and $23,446 infliximab. Cost per treated patient in RA (55% of patients) ranged from $18,888 abatacept to $22,158 infliximab and in psoriasis, (20% of patients), from $21,034 adalimumab to $31,478 ustekinumab. CONCLUSIONS:   Based on drug utilization from this US managed care population, of agents approved for all indications, etanercept had the lowest cost per treated patient across all indications.  In RA, abatacept had the lowest cost, whereas infliximab had the highest.