Thirty-four percent of U.S. patients received wrong medication, improper treatment or incorrect or delayed test results during the last two years, the Commonwealth Fund found.

Thirty percent of Canadian patients reported similar medical errors, followed by 27 percent of those in Australia, 25 percent in New Zealand, 23 percent in Germany and 22 percent in Britain, the health care foundation said.

"Driven up by relatively high medication and lab or test errors, at 34 percent, the spread between the United States and the countries with the lowest error rates was wide," Cathy Schoen, senior vice president of Commonwealth Fund, wrote in the journal Health Affairs, which published the study on its Web site.

The Commonwealth Fund says its mission is to support independent research on health care issues.

Researchers, who conducted the poll between March and June, questioned adults who had experienced some kind of serious condition that required "intense" medical treatment or had been hospitalized for something other than routine pregnancy.

"Overall patient experiences often paint a picture of no person or team responsible for ensuring that care is coordinated and continuous, with a focus on patients' needs," Schoen said.

Patients in the United States reported the highest rate of disorganized care at doctor's offices -- 33 percent -- followed by Germany with 26 percent, Canada with 24 percent and New Zealand with 21 percent. Patients in Britain and Australia reported 19 percent.

U.S. patients also stood out for shouldering more medical expenses than those in the other countries. More than half said they did not take their medicines or see a doctor because of costs.

In the United Kingdom, where health care is subsidized by the government, 13 percent of patients polled said they went without care.

Overall, "shortfalls were particularly evident for people when discharged from the hospital, and for patients seeing multiple physicians," Schoen said.

Between 700 and 750 adults were surveyed by telephone in Canada, Australia and New Zealand, and about 1,500 in Britain, Germany and the United States.

The poll's error margin was plus or minus 4 percentage points in Australia, Canada and New Zealand, 3 points in Germany and the United States and 2 points in Britain.