Background: The transition into university is the first major life transition an individual faces. It is often associated with increases in acute stress and psychological distress (Gall et al., 2000), but can be mitigated through physical activity (PA) (Bray & Born, 2004). Our knowledge of students' stress and distress, however, has been largely limited to cross-sectional or prospective studies with substantial gaps between assessment periods. The current study aims to examine patterns of stress and distress throughout students' first semester at university, and the potential impact of a PA-based intervention. Methods: Participants included 70 first-year university students (Mage=17.85+/-0.51, 49 females), enrolled into an intervention (n=28) or control condition (n=42) as part of a quasi-experimental trial. All participants completed weekly assessments of perceived stress, psychological distress, and PA. Mixed effects modeling were used to examine patterns of stress and distress as primary outcomes of interest. Results: Findings indicate a significant main effect in time for stress (Estimate=-.02, p=.025), while approaching significance for psychological distress (Estimate=-.06, p=.055). Time by condition interactions were not significant (p's .17-.20), though there were larger decreases stress and distress over time for those in the intervention condition. Conclusion: Findings suggest that university students experience the highest amount of psychological distress and stress upon immediate entry into university, and that a linear decline occurs as the semester progresses. PA-based interventions may be effective in helping decrease stress and distress, but efforts may need to target the acute transition into university. Future studies with larger samples are required.