About 10 percent of doctors recently surveyed said they hadn't always been honest with their patients, according to new research published in the journal Health Affairs.  They were most likely to lie about whether they  committed any significant medical errors and whether they have a financial relationship with a drug or device company.

Researchers led by Dr. Lisa Iezzoni, director of the Massachusetts General Hospital's Mongan Institute for Health Policy, gathered survey data from nearly 1,900 physicians from different specialties.  They asked the doctors what information they thought they needed to disclose to patients.

Approximately 33 percent of doctors said they didn't completely agree with telling patients about serious medical errors, and nearly 4o percent said they didn't believe they always had to inform patients of any financial ties to drug or device companies.  About 20 percent of the doctors surveyed said they didn't think they always had to be entirely truthful with patients.  More than half of the doctors also said they did not tell their patients about all the risks or benefits of specific  medical procedures.

The doctors were also asked about patient privacy, and about one-third said they shared confidential medical information with people who were not authorized to have it.

"Our findings raise concerns that some patients might not be receiving complete and accurate information from their physicians," the authors wrote.  "The effects of these communication lapses are unclear, but they could include patients' lack of information needed to make fully informed decisions about their health care."

The Charter on Medical Professionalism, a document that requires that doctors be open and honest when communicating with patients, is supported by more than 100 professional medical groups worldwide, but the study authors said "substantial percentages of U.S. physicians did not completely endorse these precepts."

Women, minorities and surgeons were more likely to follow the charter's principles of honesty and openness.

It isn't entirely clear why doctors lie  under these circumstances or why there are gender, specialty and ethnic differences, the authors said.

"Some physicians might not tell patients the full truth, to avoid upsetting them or causing them to lose hope," they wrote.

And doctors may not want to disclose medical errors if their mistakes didn't cause any significant harm to patients, but, according to the authors, "informing patients fully about medical errors can reduce anger and lessen patients' interest in bringing malpractice lawsuits."

The researchers were also troubled by the finding that doctors didn't always believe it's important to divulge their dealings with drug and device manufacturers.  Under the 2009 Physician Payment Sunshine Act, companies will be required to report payments to doctors of $10 or more beginning in 2013.

"Physicians who do not support public disclosure might resist communicating this information to inquiring patients or might make these conversations difficult," the researchers said.

Study co-author Eric Campbell, director of research at the Mongan Institute for Health Policy, told ABC News he and his colleagues plan to further explore the reasons   doctors support nondisclosure as well as why there are differences among doctors of different sexes, ethnicities and specialties.

"Until we know what the problem is, we can't come up with ways to fix it," Campbell said.