A high-risk pool was a state-run insurance program that provided coverage to people who couldn't get individual health insurance because of pre-existing conditions. Before the ACA, insurers in the individual market could, and routinely did, deny coverage to people with serious health histories. High-risk pools were the safety net.
These pools typically charged premiums that were 150%–200% of standard rates, had high deductibles, imposed annual benefit caps, and sometimes excluded coverage for the very pre-existing condition that made you uninsurable elsewhere. Coverage was expensive and limited, but it was often the only option.
The ACA effectively eliminated the need for high-risk pools by requiring all individual and small group plans to accept everyone regardless of health status (guaranteed issue) and charge the same rates to healthy and sick people of the same age (community rating). Most state high-risk pools were phased out between 2010 and 2014 as ACA protections took effect.
During the transition period (2010–2014), the federal government ran the Pre-Existing Condition Insurance Plan (PCIP) as a temporary bridge for people who'd been denied coverage. PCIP closed in 2014 when the Marketplace opened and pre-existing condition protections took full effect.
The concept of high-risk pools occasionally resurfaces in health policy debates as an alternative to ACA protections. Critics of the ACA have proposed returning to a high-risk pool model, while defenders argue the pre-ACA experience showed that pools were underfunded, expensive, and failed to adequately cover the people who needed help most.
Most state high-risk pools were closed after ACA protections took effect in 2014. A few states maintain limited programs, but for the vast majority of Americans, the Marketplace with guaranteed issue has replaced the need for high-risk pools.