Before the development of medical expense insurance, patients were expected to pay all other health care costs out of their own pockets, under what is known as the fee-for-service business model. During the middle to late 20th century, traditional disability insurance evolved into modern health insurance programs. Today, most comprehensive private health insurance programs cover the cost of routine, preventive, and emergency health care procedures, and also most prescription drugs, but this was not always the case. The rise of private insurance was accompanied by the gradual expansion of public insurance programs for those who could not acquire coverage through the market.
Accident insurance was first offered in the United States by the Franklin Health Assurance Company of Massachusetts. This firm, founded in 1850, offered insurance against injuries arising from railroad and steamboat accidents. Sixty organizations were offering accident insurance in the US by 1866, but the industry consolidated rapidly soon thereafter. While there were earlier experiments, sickness coverage in the US effectively dates from 1890. The first employer-sponsored group disability policy was issued in 1911, but this plan's primary purpose was replacing wages lost because the worker was unable to work, not medical expenses.
The blurring of distinctions between the different types of health care coverage can be seen in the history of the industry's trade associations. The two primary HMO trade associations were the Group Health Association of America and the American Managed Care and Review Association. After merging, they were known as American Association of Health Plans (AAHP). The primary trade association for commercial health insurers was the Health Insurance Association of America (HIAA). These two have now merged, and are known as America's Health Insurance Plans (AHIP).
According to a 2007 study, about 59% of employers at small firms (3–199 workers) in the US provide employee health insurance. The percentage of small firms offering coverage has been dropping steadily since 1999. The study notes that cost remains the main reason cited by small firms who do not offer health benefits. Small firms that are new are less likely to offer coverage than ones that have been in existence for a number of years. For example, using 2005 data for firms with fewer than 10 employees, 43% of those that had been in existence at least 20 years offered coverage, but only 24% of those that had been in existence less than 5 years did. The volatility of offer rates from year to year also appears to be higher for newer small businesses.
States regulate small group premium rates, typically by placing limits on the premium variation allowable between groups (rate bands). Insurers price to recover their costs over their entire book of small group business while abiding by state rating rules. Over time, the effect of initial underwriting "wears off" as the cost of a group regresses towards the mean. Recent claim experience—whether better or worse than average—is a strong predictor of future costs in the near term. But the average health status of a particular small employer group tends to regress over time towards that of an average group. The process used to price small group coverage changes when a state enacts small group reform laws.