More than 14 percent of Americans lacked health insurance last year, a slightly lower share than 2004, according to federal statistics published on Wednesday.
The survey, by the National Center for Health Statistics, also found that 8.9 percent of U.S. children were not covered by health insurance.
The issue of health-insurance coverage is at the center of an extended debate over health care in the United States, which relies mostly on employers to cover workers.
On Wednesday officials in San Francisco said they were pressing ahead with plans for funding health care for 82,000 residents who do not have medical insurance, at a cost of $200 million a year.
The center's report says that in 2005, 41.2 million Americans, or 14.2 percent of the population, were uninsured when its survey was conducted. It said 51.3 million had been uninsured for at least part of the prior year and 29.2 million, or 10 percent, had been uninsured for more than a year.
The study is based on a regular survey of more than 98,300 people.
The NCHS, part of the Centers for Disease Control and Prevention, found that insurance coverage varied widely among states, from 6 percent without health insurance in Massachusetts to more than 24 percent without in Texas.
More than 70 percent of adults and 62 percent of children had private insurance coverage, while nearly 30 percent of children and 11.5 percent of adults had some sort of public insurance such as the State Children's Health Insurance Program, Medicare or Medicaid.
The numbers show a slight improvement over last year and over 1997, the NCHS said. In 1997, 15.4 percent of U.S. adults and 13.9 percent of children went without health insurance.
In 2004, 9.4 percent of children -- 7 million children under 18 years of age -- lacked health insurance, as did 14.6 percent of the population, or 42.1 million Americans of all ages.
The survey also found that diabetes and asthma are on the rise, with up to 7.4 percent of the population diagnosed with diabetes and 7.8 percent of the population with asthma.