The main aim of this study was to evaluate the physical activity (PA) levels of high school Portuguese students during physical education (PE) and investigate the association of PA levels with students' goal orientation and intrinsic motivation. Forty-six students from three high schools participated. Heart rate telemetry and pedometry were used to assess PA and the Borg rate of perceived exertion scale was used to measure perceived exertion. Thirty PE lessons were monitored. The results indicated that high school PE lessons involve low levels of PA. Students engaged in moderate to vigorous PA (MVPA) only in about one-third (29.7 minutes) of the official PE scheduled time (90 minutes) and perceived exertion as light. In general, students seemed to be positively motivated toward PE and mainly task goal orientated. Boys felt more enjoyment/interest and perceived their competence in more positive ways than girls. The number of steps and the rate of perceived exertion were associated with levels of PA measured by heart rate telemetry. Intrinsic motivation and goal orientation were not related with MVPA. (Contains 4 tables.)