After market exclusivity ends for biologic drugs, biosimilars-follow-on versions made by other manufacturers-can compete with lower prices. Biosimilars have modestly reduced prescription drug spending for US payers, but it is unclear whether patients have directly experienced any savings. In this study we assessed whether availability of biosimilar infliximab was associated with lower out-of-pocket (OOP) costs, using claims from a national data set of commercially insured patients from 2014 to 2018. We used two-part models, adjusting for patient demographics, clinical characteristics, insurance plan type, and calendar month. Compared with the reference biologic, there was no difference in the percentage of biosimilar claims with OOP costs (30.1% vs. 30.8%; adjusted odds ratio (aOR) 0.98, 95% confidence interval (CI), 0.84-1.15, P = 0.84) or the average nonzero OOP cost (median $378 vs. $538, adjusted mean ratio (aMR) 0.97, 95% CI, 0.80-1.18, P = 0.77). The percentage of claims with OOP costs was lower after biosimilar competition (30.7% vs. 35.0%, aOR 0.96, 95% CI, 0.94-0.99, P = 0.003), but average nonzero costs increased (median $534 vs. $520, aMR 1.04, 95% CI, 1.01-1.07, P = 0.004). Thus, early biosimilar infliximab competition did not improve affordability for patients. Policymakers need to better assure that competition in the biosimilar market translates to lower costs for patients using these medications.