The study prepared for the Robert Wood Foundation by the State Health Access Data Assistance Center at the University of Minnesota found the number of uninsured U.S. citizens rose by 9 million from 1996 to 2007.
At the end of the study period, 22 percent of men were uninsured, up from 19 percent, while 18 percent of women were uninsured, up from 16 percent, the report stated.
Among children, the rate of those without insurance fell by 13 percent, due to expansions of Medicaid and the Children's Health Insurance Program, the study said.
The study said 45.7 million U.S. citizens were uninsured. In addition, employees' insurance bills rose 79 percent in the study period, while wages rose 10 percent.
"The case for reform couldn't be clearer," Dr. Risa Lavizzo-Mourey, president of the Robert Wood Johnson Foundation, said in a statement.
"The rising costs of healthcare has largely been borne by workers who are not getting raises because of it and employers who are seeing these costs eat into their profit margins."