The virtues of bariatric surgery are self-evident to surgeons who perform weight-loss operations. They see the surgery as the only potentially effective treatment for those who are severely obese. It's hard to argue with that; for most of these individuals, lifestyle changes and various medical approaches have a record that can only be called dismal.

But is bariatric surgery safe? Most surgeons think so. Past studies suggest a risk of death of about 0.5 percent, an acceptable figure for major surgery. Those studies, however, were sketchy and their methodology shaky.

In a five-article package on bariatric surgery in this week's Journal of the American Medical Association, new and more credible statistics paint a much different picture—at least for some patients.

The most striking finding was a death rate much higher than expected in older patients who were studied. Within 90 days of leaving the hospital, mortality in patients ages 65 and older was almost 7 percent. That was three times the death rate for patients younger than age 65—which also was far above the accepted figure. For patients 75 years old and up, the 90-day death rate was almost 19 percent for women and nearly 20 percent for men.

But age wasn't the only thing that weighed heavily. Patients 65 and older whose surgeons did fewer than 15 weight-loss operations a year had a 90-day mortality rate of almost 14 percent. The rate was below 5 percent for surgeons who performed 15 to 35 procedures a year and about 2 percent for those who did 36 to 70 procedures. Volume does matter, as has been demonstrated repeatedly for many types of complex surgery.

That's something to keep in mind when thinking about having bariatric surgery.

An accompanying editorial called the findings "opportunities for improvement" rather than reasons to avoid the surgery. Obesity carries its own risks, the editorial observed, and weight-loss surgery can lower them—yet far fewer than 1 percent of individuals who might benefit from the operation, wrote the editorialists, have had it. Medicare currently is considering whether to pay for weight-loss surgery on obese people without an underlying condition made worse by the excess weight, such as diabetes. These studies will certainly be read with interest by Medicare's administrators.