WITH ALL THAT'S going on in the market, it would be nice to think you could leave your health care on autopilot but you'd be wrong. This October, as usual, 158 million American workers will have to make seemingly small but ultimately crucial decisions, as corporate America shifts more of its $537 billion health care burden onto workers. "People need to be more thoughtful about their choice than in the past several years," says Jay Savan, a principal with the professional-services firm Towers Perrin especially if they don't want to get stuck with hefty bills. Some tips on being choosy:

Watch for hidden costs

Read the fine print: One trend Savan expects to see grow is surcharges sometimes as high as $150 each month for employees who opt to cover a spouse or child who could get benefits elsewhere. And the consultancy Mercer Health & Benefits estimates that 25 percent of large employers will offer prescription-drug plans that make employees pay a portion of drug costs instead of a simple copay. That'll sting if you're on, say, a $14,000 cancer drug.

Snag incentives

Being healthy can be good for a lot more than your waistline. In 2007 almost one in four large companies offered workers incentives for healthy behavior, a trend experts say will mushroom in 2009. Alexander Domaszewicz, a principal at Mercer, says he's seen perks such as lower deductibles and even a month of benefits for healthy decisions like losing weight. Don't lie, though: "That's like stealing from the company," Domaszewicz says, and can be a fireable offense.

Don't fear health-savings accounts

With caps on out-of-pocket costs and coverage for most preventive screenings, these plans can be a good deal, especially for the very sick or for very healthy consumers looking to sock away pretax funds. Balance the huge amount you'll save in premium costs against your exposure, Savan says. Many insurers' Web sites can help evaluate various plans.

• For more SmartMoney Magazine features, turn to the October issue.