Regulating stop-loss coverage may be needed to deter self- insuring small employers from undermining market reforms.

As implementation of the Affordable Care Act reshapes the US health insurance market, state policy makers should be prepared to revisit regulation of stop-loss coverage-a form of reinsurance-for small businesses. Aspects of the reform law could motivate small businesses to self-insure, rather than participate in state-regulated markets either inside or outside the new health insurance exchanges. If younger or healthier groups self-insure, premiums for insured plans might rise to an extent that could seriously impair the regulated market. States can influence small businesses to participate in the regulated market by making it more difficult or costly to obtain stop-loss coverage, which self-funded employers rely on to protect their businesses from catastrophic medical costs incurred by one or more insured workers. States can limit the comprehensiveness of stop-loss coverage, ban stop-loss coverage outright, or regulate it as they do primary coverage. But states need federal guidance about how to exercise this authority if they are to promote, or prevent the undermining of, important aspects of federal health care reform.