About half of all the people in the United States will develop one or more mental disorders in their lifetimes, according to the latest national survey. During any year, one of every four people in this country fits the definition of “mentally ill.”

Most of these disorders are mild, the census-like survey found. Mild or severe, most of them start before or during adolescence, and most patients wait years for treatment or go untreated. Even when treatment is available, it is not likely to be very good.

“It has been a decade since the last national survey of mental health in this country was taken,” says Ronald Kessler, a professor of health care policy at Harvard Medical School, who directed both surveys. “Many important advances have been made in terms of new medications, public attitudes, and financing of treatment. Because of this, treatment has increased dramatically. We were hoping to see a decrease in disorder prevalence, but we did not. Also, quality of treatment was found to be low.”

Four articles in the June issue of Archives of General Psychiatry and one in the June 16 issue of the New England Journal of Medicine report survey results. A key finding is that those who did receive health care often did not get treatment consistent with even minimum accepted standards. Only about 13 percent of patients with mental health problems received adequate care.

The researchers were struck and disappointed to learn that many people turn to nonmedical treatments without proven benefit. About one out of three patients relied on sources such as spiritual advisers and Internet groups. “You wouldn’t rely on your priest for treatment if you had breast cancer,” commented Thomas Insel, director of the National Institute of Mental Health, major supporter of the $20 million survey.