Background: U. S. HIV treatment guidelines recommend branded once-daily, 1-pill efavirenz-emtricitabine-tenofovir as first-line antiretroviral therapy (ART). With the anticipated approval of generic efavirenz in the United States, a once-daily, 3-pill alternative (generic efavirenz, generic lamivudine, and tenofovir) will decrease cost but may reduce adherence and virologic suppression. Objective: To assess the clinical effect, costs, and cost-effectiveness of a 3-pill, generic-based regimen compared with a branded, co-formulated regimen and to project the potential national savings in the first year of a switch to generic-based ART. Design: Mathematical simulation of HIV disease. Setting: United States. Patients: HIV-infected persons. Intervention: No ART (for comparison); 3-pill, generic-based ART; and branded ART. Measurements: Quality-adjusted life expectancy, costs, and incremental cost-effectiveness ratios (ICERs) in dollars per qualityadjusted life-year (QALY). Results: Compared with no ART, generic-based ART has an ICER of $ 21 100/QALY. Compared with generic-based ART, branded ART increases lifetime costs by $ 42 500 and per-person survival gains by 0.37 QALYs for an ICER of $ 114 800/QALY. Estimated first-year savings, if all eligible U. S. patients start or switch to generic-based ART, are $ 920 million. Most plausible assumptions about generic-based ART efficacy and costs lead to branded ART ICERs greater than $ 100 000/QALY. Limitation: The efficacy and price reduction associated with generic drugs are unknown, and estimates are intended to be conservative. Conclusion: Compared with a slightly less effective generic-based regimen, the cost-effectiveness of first-line branded ART exceeds $ 100 000/QALY. Generic-based ART in the United States could yield substantial budgetary savings to HIV programs.