© 2016 by the American Association for the Study of Liver Diseases. From December 2012 to March 2014, three randomized trials, each implementing a unique intervention in primary care settings (repeated mailing, an electronic health record best practice alert [BPA], and patient solicitation), evaluated hepatitis C virus (HCV) antibody testing, diagnosis, and costs for each of the interventions compared with standard-of-care testing. Multilevel multivariable models were used to estimate the adjusted risk ratio (aRR) for receiving an HCV antibody test, and costs were estimated using activity-based costing. The goal of this study was to estimate the effects of interventions conducted as part of the Birth-Cohort Evaluation to Advance Screening and Testing for Hepatitis C study on HCV testing and costs among persons of the 1945-1965 birth cohort (BC). Intervention resulted in substantially higher HCV testing rates compared with standard-of-care testing (26.9% versus 1.4% for repeated mailing, 30.9% versus 3.6% for BPA, and 63.5% versus 2.0% for patient solicitation) and significantly higher aRR for testing after controlling for sex, birth year, race, insurance type, and median household income (19.2 [95% confidence interval (CI), 9.7–38.2] for repeated mailing, 13.2 [95% CI, 3.6–48.6] for BPA, and 32.9 [95% CI, 19.3–56.1] for patient solicitation). The BPA intervention had the lowest incremental cost per completed test ($24 with fixed startup costs, $3 without) and also the lowest incremental cost per new case identified after omitting fixed startup costs ($1691). Conclusion: HCV testing interventions resulted in an increase in BC testing compared with standard-of-care testing but also increased costs. The effect size and incremental costs of BPA intervention (excluding startup costs) support more widespread adoption compared with the other interventions. (Hepatology 2017;65:44-53).