Objective: To compare the prevalence and trajectories of risky health behaviors in sexual minority (SM; lesbian/gay/bisexual/questioning/asexual) versus heterosexual undergraduates across their first year of post-secondary. Participants: First-year undergraduates (N = 704, M[subscript age] = 17.97 years, 24% SM) from a midsized Canadian university. Methods: Students completed monthly (September-April) online questionnaires assessing substance use (binge drinking, tobacco, cannabis, illicit drug use) and disordered eating (binge eating, fasting, purging). Results: At the outset of the academic year, SM students endorsed more frequent cannabis use, illicit drug use, fasting, and binge eating, but less frequent tobacco use, versus heterosexual students. Over the year, SM students' binge drinking frequency declined less than that of heterosexual students, but their illicit drug use decreased while that of their heterosexual peers increased, and all students reported declining disordered eating frequency. Conclusions: Campus wellness initiatives for SM students should offer prevention and harm-reduction strategies prior to or shortly after their arrival on campus.