The authors investigated vigorous physical activity and psychological well-being during transition from high school to first-year university in a sample of 145 Canadian undergraduates. Participants completed retrospective measures assessing vigorous physical activity during their first 2 months at university and their last 2 months at high school as well as measures assessing psychological well-being. According to nationally recommended (US Department of Health and Human Services) standards, two thirds (66.2%) of students reported adequate levels of vigorous activity in high school, whereas significantly fewer (44.1%) met the standard during their first 8 weeks at university. One third of students were active in high school but became insufficiently active once at university; 33% were active at both times; 23% consistently fell short of recommended levels; and only 11% became active once at university. Students who had become insufficiently active reported higher levels of fatigue and lower levels of vigor compared with those who continued to be active.