The Congressional Budget Office (CBO), a nonpartisan agency of Congress, made official projections of the Affordable Care Act's impact on insurance coverage rates and the costs of providing subsidies to consumers purchasing health plans in the insurance marketplaces. This analysis finds that the CBO overestimated marketplace enrollment by 30 percent and marketplace costs by 28 percent, while it underestimated Medicaid enrollment by about 14 percent. Nonetheless, the CBO's projections were closer to realized experience than were those of many other prominent forecasters. Moreover, had the CBO correctly anticipated income levels and health care prices in 2014, its estimate of marketplace enrollment would have been within 18 percent of actual experience. Given the likelihood of additional reforms to national health policy in future years, it is reassuring that, despite the many unforeseen factors surrounding the law's rollout and participation in its reforms, the CBO's forecast was reasonably accurate.