During the same time period, the male-female earnings gap in the general population closed from 28 percent to 15 percent, the researchers found.
Study author Anupam Jena, assistant professor of healthcare policy and medicine at Harvard Medical School and general internist at Massachusetts General Hospital -- said while the income gap among physicians held steady at about 25 percent, the percentage of female physicians rose from 10 percent to 28 percent, and women now make up about half of medical school graduates.
"Given that in the overall economy women have now closed more than half the gender income gap that was present in the late 1980s and given that many more physicians are now women, we were surprised to find such persistent income disparity between men and women in medicine," Jena said in a statement.
Jena and colleagues at the University of Southern California and Harvard Kennedy School used nationally representative data from the Current Population Survey, collected by the U.S. Census Bureau and the U.S. Bureau of Labor Statistics.
The researchers compared trends in male and female physician earnings with earnings of other healthcare professionals and with the general population during three periods from 1987-2010. The researchers corrected for the number of hours worked and adjusted all of the figures to 2010 dollar amounts.
There are several causes for the disparity in pay, the researchers said. Women are more likely than men to choose specialties like pediatrics and family medicine that offer more patient interaction, but are often lower paying, but it's unclear whether female physicians chose specialties out of personal preference, or because they face obstacles in choosing other specialties.
The study, published in Internal Medicine, did not collect data about physician specialty, so the study did not correct for differences in specialty pay.
Notable deaths of 2014 [PHOTOS]