Motivated by the regulatory changes introduced by the Dodd–Frank Wall Street Reform and Consumer Protection Act of 2010, this study investigates its impact on the cost efficiency of US banks. Using a parametric cost frontier methodology previously linked to bank failure risk, the analysis reveals a 13% average decline in cost efficiency under the new regulatory framework. The study also examines the Act's potential heterogeneous effects across banks of different sizes, revealing that while larger banks are typically more efficient, the stricter regulatory oversight imposed on them by the Dodd–Frank Act reduced the efficiency gap with smaller banks.