Aim and objectives: In the USA, undergraduate students gain more weight in the first year in college than at any other point in their lives. However, the factors that predict their weight gain are unknown. The purpose of this study was to explore the predictors of weight gain among first-year college students at a US college over a 3-month period. Design: Correlational longitudinal study using baseline and follow-up self-report survey data. Setting: A private college in the Northeastern USA. Methods: A total of 110 first-year college students were invited to complete both baseline and follow-up surveys 3 months apart. The baseline survey examined participants' knowledge, self-efficacy, attitudes, intentions and practices regarding physical activity, diet and stress management. The follow-up survey evaluated barriers to diet and exercise practices. Results: Knowledge, attitudes, intentions and behavioural practices did not predict weight change. However, students who gained weight perceived significantly more personal and environmental barriers than those who did not change weight on the following variables: lack of motivation to exercise, no time to eat healthily, perception of lack of healthy food options and impact of bad weather on exercise. Conclusion: Even living in the same college environment, students perceive environmental barriers differently, which was associated with body weight gain. Health education and promotion professionals should guide students to overcome barriers to healthy eating and exercise, as well as making the campus environment more conducive to healthy behaviour.