Mark Lachs says an epidemic of thefts and fraud targeting the elderly - by lawyers, financial advisers, family members, and others - is fast becoming a national crisis.

He should know.

Lachs, a geriatrician and social scientist at Weill Cornell Medical College in New York, is a leading expert on the financial and physical abuse of America's aging population. He and a few other social scientists have begun to provide the first credible scientific reports on the extent of fraud and other financial exploitation aimed at the elderly.

Their work suggests that millions are victimized every year. But only a fraction of the incidents ever comes to the attention of authorities.

"There are millions and millions of people who are affected, and it is enormous in its scope; you go to a dinner, and everyone has a . . . story," Lachs says. "If this were a disease, we would probably say it is an epidemic."

Lachs, who did undergraduate work and a medical residency at the University of Pennsylvania, is a clinical practitioner in New York. He is also known internationally for his elegantly designed and penetrating epidemiological studies. His groundbreaking 1998 work on mortality rates of elderly victims of financial and physical mistreatment showed that victims die at a rate three times faster than those who have not been abused.

Lachs and his colleagues drew attention again in March with a study, based in part on a phone survey of 4,000 people over age 60 in which 4.2 percent of respondents said they had been the victims of financial fraud or exploitation in the preceding year.

The implications are sobering. Projected on a national stage, the results suggest that at least 2.5 million people over 60 are victimized by family members, financial advisers, scammers, and others. Even Lachs' tally was likely an undercount because elderly people suffering from severe mental decline, a group at high risk for being preyed upon, were not polled.

The resources lost in those schemes will not be passed down to heirs or donated to charities. Nor can the assets pay for nursing-home care. Elderly victims who lose their savings often turn to Medicaid, the government health-care program.

Just as troubling is Lachs' corollary finding: Only a tiny percentage of fraud cases ever come to the attention of authorities.

When Lachs and his colleagues compared the results of the phone survey with reports to law enforcement and social-service agencies, they concluded only one in 44 cases of abuse is reported.

"I have no doubt," Lachs said, "that financial fraud is by far the most common form of abuse of the elderly."

For years, the primary source of data on the physical abuse and financial exploitation of the elderly came from the National Center on Elder Abuse, which since the late 1980s has culled information from reports by Adult Protective Services.

But data sets differed from one state to another, and not all states participated. Moreover, the data were collected for program management and funding requests, not scientific inquiry.

Only in the last few years have social scientists and physicians such as Lachs begun to understand how much abuse is inflicted on the elderly.

The problem is getting worse. The Government Accountability Office says reports of fraud and other bad treatment are burgeoning as the aging of America's population accelerates.

In 2008, University of Chicago researchers interviewed 3,000 people between the ages of 57 and 85 asking whether they had been subjected to physical or financial mistreatment in the preceding year; 3.5 percent said that a caregiver, relative, or financial adviser had improperly taken their money. (Again, the research excluded those suffering from dementia and other mental decline.)

Similar findings emerged from a Justice Department study conducted by Ron Acierno, a professor of psychiatry and behavioral sciences at the Medical University of South Carolina. In a random phone survey of 6,000 people over 60, one in 20 reported suffering financial mistreatment at the hands of relatives in the preceding year.

"The majority of the research . . . has tended to obscure the issue of elder abuse rather than enlighten," Karl Pillemer, a professor of human development at Cornell University and one of the first social scientists to quantify abuse of the elderly, said of past studies. Lachs "was one of the few physicians who would go to visit protective services. He combined his training as a physician and in public health and epidemiology, which really makes him a unique figure."

The day his grandfather died of kidney cancer 41 years ago, 10-year-old Mark Lachs wept inconsolably.

Other boys may have idolized race-car drivers or athletes, but Lachs' hero growing up was his feisty grandfather. Harold Fenster filled an emotional gap that opened wide when Lachs' parents split, and young Mark went to live with his mother.

Fenster taught his grandson how to body surf, ride a bike, and throw a baseball. Witty, athletic, and fun-loving, the prominent trial lawyer radiated authority.

"He was a tough guy physically, and he was a tough guy intellectually, and he loved me," Lachs said.