SAN DIEGO — Mexicans who recently arrive in the United States — many illegally — are far less likely to visit hospital emergency rooms than long-term Mexican immigrants or people born in the United States, a report said Thursday.

Researchers at Mexico's National Population Council and the University of California found that only 9.8 percent of Mexican adult migrants living in the United States 10 years or less visited an emergency room in the past year. That's less than half the rate among people born in the United States — 19.9 percent for people of Mexican ancestry born in the United States and 20 percent for U.S.-born whites.

Among Mexican immigrants living in the United States more than 10 years, 13.7 percent visited an emergency room in the previous year, according to an analysis of data collected in 2000 for the U.S. National Health Interview Survey.

The findings run counter to a widespread belief that illegal immigrants are a major burden on emergency rooms, said Mario Gutierrez, program director of rural and agricultural health at The California Endowment, a private health foundation that co-sponsored the study.

The study draws on data from the U.S. Census, U.S. National Health Survey and Mexican government to compare health care access in the United States between new arrivals from Mexico, long-staying Mexican immigrants and native born.

The health survey data has been available a few years, but the findings are new, said Steven Wallace, associate director of UCLA Center for Health Policy Research and a co-author of the report.

"The data was not released yesterday but it was never looked at in this way," he said.

Many new arrivals are in the United States illegally. More than three-quarters of an estimated 440,000 annual arrivals from 2001 to 2004 crossed illegally, according to the Mexican government. Among migrants who arrived within the past 10 years, only 5.5 percent are U.S. citizens, according to 2004 U.S. Census data.

The report found migrants arrive in relatively good health. Only 6.8 percent considered themselves in fair or poor health, much lower than other groups. Only 2.6 percent were diagnosed with diabetes, also much lower than other groups.

Fewer new arrivals were found to seek medical care. More than 33 percent of women 18 to 64 years old had no pap smear in three years, higher than other groups. Only 29.7 percent of adults visited a dentist in the past year, much lower than other groups.