The Chicago Tribune investigation also found that the Joint Commission on Accreditation of Healthcare Organizations underreports patient deaths from infections and hospital errors.

The Oakbrook Terrace, Ill.-based commission is empowered by Congress to ensure the quality and safety of hospitals. It touts its surveys as an assurance that hospitals are clean, adequately staffed and provide superior care.

But the Tribune report, in Sunday editions, found the commission often fails in its role. Among the findings:

- Less than 1 percent of hospitals failed to receive accreditation from the commission in the last 17 years, and some hospitals received accreditation scores even in the midst of public health crises.

For example, Palm Beach Gardens Medical Center in Florida retained its high ranking even after federal public health investigators found that its patients were in "immediate jeopardy" because of infection-control deficiencies.

- Hospital inspection dates are announced up to three months in advance, giving medical centers time to upgrade conditions. The commission also allows hospitals to choose the patient files that will be reviewed by inspectors.

- The commission uses a voluntary reporting system that underestimates the number of avoidable patient deaths.

For example, the organization documented just 12 cases of preventable hospital-borne infections since 1995. The Tribune, using other government sources, found about 75,000 such deaths in just one year.

Commission officials acknowledged flaws in the survey process.

"We have missed things," said Dr. Dennis O'Leary, commission president. "These are fallible systems."

But O'Leary also defended the commission, saying its methods have helped it earn hospital officials' trust and cooperation.

The accreditation process is being overhauled in response to criticism from the federal government and some hospitals, O'Leary said. The changes, which will include tougher standards and more focus on patient care, are scheduled to take effect in 2004, he said.