When workers throughout the country get the chance to make changes to their health insurance coverage this fall, some may find that their employer is offering a new option: health savings accounts.

These accounts, which are coupled with high-deductible insurance plans, allow people to put aside money tax free — up to $3,000 for individuals and $5,950 for families in 2009 — to help pay for medical expenses that are not covered by insurance, including things like over-the-counter medications.

One feature that has helped fuel their popularity is that the unused account balance can accumulate and earn tax-free interest, allowing people to save in years of low medical expenses to cover years when health care costs are higher. HSA account holders over 55 can also make increased payments until they are eligible for Medicare (usually at age 65), making the accounts another arrow in their retirement-planning quiver.

Created in 2004 as part of an effort to encourage consumers to control the amount they spend on health care, HSAs are administered by banks, credit unions, insurance companies and some stand-alone companies. They have jumped in popularity, with surveys showing the number of people enrolled in HSAs topping 6.1 million in 2008, from 438,000 in September 2004. Some industry observers forecast more than 10 million people will enroll for 2009, as the number of employers that offer them grow.

According to business consulting firm Mercer LLC, 19 percent of employers will offer HSA-eligible plans as a way to lower their costs in 2009. "As employers continue to seek ways to maintain health care coverage, the lower premiums that are associated with high-deductible health plans are very attractive," said David Josephs, head of J.P. Morgan's consumer directed health care business, which has more than 300,000 HSA account holders with more than $400 million in assets.

While HSAs are more likely to be offered by large companies, they can be an option for small and mid-size businesses as well. Both workers and their employers can contribute to the HSA, although the contribution cap remains the same regardless of who funds the savings. Individuals may also open HSAS if they buy eligible high-deductible insurance plans. Regardless of whether they are opened individually or through an employer, HSAs are owned by the account holders, who do not lose the money if they switch jobs or insurance coverage in later years.

But there are concerns to watch out for, most notably the high deductibles associated with the insurance plans — meaning that consumers will pay more out-of-pocket expenses before their insurance coverage kicks in. "For the individual, it can make sense if you really don't expect to have a lot of expenses," said Annette Ramirez de Arellano, a researcher with Public Citizen, a consumer advocacy group. "Or, if you don't mind paying the deductibles, because you'd rather have control over the income and you want to roll over what's left over."

But for people who have high medical expenses or those who might avoid getting medical care because of the deductible, HSAs are not likely a good choice, she said.

There's also the question of whether you can afford to take advantage of the HSA feature by contributing to the savings account, rather than just taking advantage of the low premiums associated with the high deductible insurance, noted Gail Shearer, director of health policy analysis for the Washington office of Consumers Union.

In fact, a report by the U.S. General Accountability Office showed that nearly half of the people enrolled in HSA-eligible health care plans from 2005 to 2007 did not open an HSA, and about a quarter had no plans to do so. The implication being that the majority enrolled in the plans simply to take advantage of the lower premiums, leaving them with no back-up to cover their high deductible or other health-care costs.