We studied the incidence of injury caused by weight training in junior and senior high school football players. Three hundred fifty-four subjects completed a retrospective injury questionnaire; histories were confirmed for high school athletes. Cumulative incidence and incidence rates were determined for injuries causing more than 7 days of missed participation. The cumulative incidences of injuries were as follows: all athletes, 7.6% (27/354); junior high school athletes, 7.1% (7/98); high school freshman/junior varsity athletes, 9.4% (15/159); and high school varsity athletes, 5.2% (5/97). The total incidence rate was 0.082 injuries per person-year, with 0.11 injuries per person-year in junior high school athletes, 0.091 injuries per person-year in high school freshman/junior varsity players, and 0.051 injuries per person-year in high school varsity players. Differences in the incidence measures among groups were not statistically significant. The most common injury type was a strain (74.1%), and the most common site was the back (59.3%). Certain exercise apparently caused more back injuries in older athletes.