America teenagers are smoking and drinking less than they were 15 years ago, fewer have sex and the number who carry weapons has fallen, a survey found.

The percentage of high school students who engaged in these and other risky behaviors fell from 1991 to 2005, according to findings released today by the U.S. Centers for Disease Control and Prevention in Atlanta. Alcohol use, for example, fell to 43% last year from 51% in 1991.

Almost 14,000 students took part in the 2005 National Youth Risk Behavior Survey, which is conducted every two years in public and private high schools across America. The data are used to evaluate trends in risky behaviors as a way to shape school health programs.

“We’re delighted that we’re seeing some progress, but the realities are that the risk behavior levels are just way too high,” the director of CDC’s division of adolescent and school health, Howell Wechsler, said on a conference call with reporters yesterday. “We have a lot more work to do.”

CDC officials called for more persistent efforts to put an end to teenage habits that they said may cause difficulties, injury or death if they are carried on into adulthood. For instance, the survey found that marijuana use rose to 20% in 2005 from just 15% in 1991, and cocaine use jumped to 3.4 percent from 1.7%.

Mr. Wechsler said he was also concerned about racial and ethnic disparities among risky behaviors reported in the survey. For example, black students were more likely to be sedentary or engage in sexual risk behaviors, while more white students were frequent smokers or engaged in heavy drinking.