CAMBY, Ind. — Until the fourth trip to the hospital in 1998, Zachery Dorsett's parents thought their son was an average child who was having trouble getting over a passing illness. He was 7 months old, and it was his second case of pneumonia.

Sharon and Arnold Dorsett were concerned about Zachery's health, but they were not worried about the financial consequences. They were a middle-income couple, with health insurance that covered 90 percent of doctor bills and most prescription drug costs.

Then the bills started coming in. After a week in the hospital, the couple's share came to $1,100 — not catastrophic, but more than their small savings. They enrolled in a 90-day payment plan with the hospital and struggled to make the monthly installments of nearly $400.

But Zachery, who was eventually found to have an immune-system disorder, kept getting sick, and the expense of his treatment — fees for tests, hospitalizations, medicine — kept mounting, eventually costing the family $12,000 to $20,000 a year. Earlier this year, the Dorsetts stopped making mortgage payments on their house outside Indianapolis. In March, they filed for bankruptcy.

Never have patients had so many medical options to extend, enrich or alter their lives. But these new options are expensive, and with them has come a change for which many Americans — even those with health insurance — are financially ill-prepared.

After decades in which private and government insurance covered a progressively larger share of medical expenses, insurance companies now are shifting more costs to consumers in the form of much higher deductibles, co-payments or premiums.

At the same time, Americans are saving less and carrying higher levels of household debt, and even insured families are exposed to medical expenses that did not exist a decade ago. Many do not realize how vulnerable they are until the bills arrive.

Lawyers and accountants say that for the more than 1.5 million American families who filed for bankruptcy protection last year, the most common causes were job loss and medical expenses. New bankruptcy legislation, which went into effect Monday, requires middle-income debtors to repay a greater share of their debt.

The Dorsetts' filing came after years of accumulating relatively modest bills, often just co-payments on doctor visits or prescriptions. Almost since Zachery's birth, they had finished each year with more credit-card debt than they had the year before. Even when they took out a second mortgage to pay off their credit cards, by the end of the year they were in debt again.

On a late summer morning, Sharon Dorsett, now 32, sat with her son at St. Vincent Children's Hospital in Indianapolis as a treatment made from blood plasma dripped into his left arm, supplying the antibodies that his immune system does not produce. The monthly infusion costs $54,000 a year, of which the Dorsetts will pay more than $5,000.

For the Dorsetts, this is what the end looked like, according to the family's bankruptcy filing: They had $1,431 in their checking and savings accounts; they owed $29,146 on various credit cards; and after refinancing their house to pay down their credit cards, they could no longer afford the payments on their house or car. Arnold Dorsett, 40, who works on commercial heating and air-conditioning systems, sometimes stitching together 90-hour weeks, earns $68,000 a year.

As the bills mounted, it was Sharon Dorsett who forced her husband to acknowledge that he could not simply work more hours. "I showed him, even if I went back to work, we'd still be in debt in 10 years," Sharon Dorsett said. "Our kids could not go to college."

Though health-care costs have been rising for decades, changes in insurance starting around 2001 have put more pressure on consumers, especially those who need the most treatment, said Paul Ginsburg, president of the Center for Studying Health System Change, a nonpartisan research group financed primarily by the Robert Wood Johnson Foundation.

The families driven into bankruptcy by these costs include those dealing with both rare and common medical conditions — and others who simply saved too little or owed too much, in the false confidence that there would not be unforeseen medical problems, or that their insurance would protect them.

From 2000 to 2005, employees in the most common type of insurance plan, known as preferred-provider organizations, saw their premiums for individual coverage rise 76 percent, to $603 from $342, while their deductibles — the amount they pay out of pocket before insurance kicks in — rose almost 85 percent, to $323 from $175, according to the Kaiser Family Foundation. By 2003, a survey by the Center for Studying Health System Change estimated that 20 million American families had trouble paying their medical bills. Two-thirds of these had health insurance.

Shortly after Zachery was born, his parents knew something was not right. He got the same illnesses or infections as other children, but while others got better, he would get worse. He needed follow-up doctor visits, refills on prescriptions, X-rays, CAT scans — each time ringing up co-payments of $10, $15, $30 or more.

Finally, Sharon Dorsett asked one of the hospitals for assistance. "They said all I could do was go to churches," she said. "Which is worse, filing for bankruptcy or — I'm going to say it — begging at churches?"

Since the couple filed for bankruptcy protection in March, the creditors have stopped calling. The Dorsetts filed for — and were granted — protection under Chapter 7, which means that a trustee could liquidate their assets to pay their creditors. But as in most Chapter 7 cases, there are no assets.

In the meantime, since they are resigned to losing their house, they are putting aside the money that would have gone to the mortgage for the next round of big expenses. For the first time since Zachery's birth they are saving money.

Even with their debts cleared for the moment, there are no guarantees that the Dorsetts will be able to stay above water. The immune globulin may keep Zachery out of the emergency room this winter, or it may not. They have no credit to buffer unforeseen expenses.

Sharon Dorsett observed: "If we get another house for under $800 a month; if nothing else happens; if the treatments work — we'll make it."