For a rapidly growing share of older Americans, traditional ideas about life in retirement are being upended by a dismal reality: bankruptcy.

The signs of potential trouble — vanishing pensions, soaring medical expenses, inadequate savings — have been building for years. Now, new research sheds light on the scope of the problem: The rate of people 65 and older filing for bankruptcy is three times what it was in 1991, the study found, and the same group accounts for a far greater share of all filers.

Driving the surge, the study suggests, is a three-decade shift of financial risk from government and employers to individuals, who are bearing an ever-greater responsibility for their own financial well-being as the social safety net shrinks.

The transfer has come in the form of, among other things, longer waits for full Social Security benefits, the replacement of employer-provided pensions with 401 savings plans and more out-of-pocket spending on health care. Declining incomes, whether in retirement or leading up to it, compound the challenge.

Cheryl Mcleod of Las Vegas filed for bankruptcy in January after struggling to keep up with her mortgage payments and other expenses. “I am 70, and I am working for less money than I ever did in my life,” she said. “This life stuff happens.”

As the study, from the Consumer Bankruptcy Project, explains, older people whose finances are precarious have few places to turn. “When the costs of aging are off-loaded onto a population that simply does not have access to adequate resources, something has to give,” the study says, “and older Americans turn to what little is left of the social safety net — bankruptcy court.”

“You can manage O.K. until there is a little stumble,” said Deborah Thorne, an associate professor of sociology at the University of Idaho and an author of the study. “It doesn’t even take a big thing.”

The forces at work affect many Americans, but older people are often less able to weather them, according to Professor Thorne and her colleagues in the study. Finding, and keeping, one job is hard enough for an older person. Taking on another to pay unexpected bills is almost unfathomable.

Bankruptcy can offer a fresh start for people who need one, but for older Americans it “is too little too late,” the study says. “By the time they file, their wealth has vanished and they simply do not have enough years to get back on their feet.”