In the month before the survey 19.5 percent of students had smoked cigarettes, 9.7 percent had driven a car after drinking, and 17.5 percent had carried a weapon.
Among the 34.2 percent of students who were sexually active, 38.9 percent had not used a condom the last time they had sex.
In the year before the survey, 13.8 percent of students had seriously considered suicide and 6.3 percent had attempted it.
The percentage of students who were obese increased from 10.7 percent in 1999 to 12 percent in 2009.
According to the authors, the findings apply only to teens attending high school.
In addition, they wrote, the amount of under- or over-reporting could not be determined. And body mass index was calculated using self-reported height and weight, which tends to underestimate rates of obesity and overweight.