Background: Students in the United States gain weight significantly during their first year of university, but limited data is available for Australian students. Methods: This 12-month observational study was conducA 12-Month Prospective Observational Study of Body Weight, Dietary Intake, and Physical Activity Levels in Australian First-Year University Studentsted to monitor monthly body weight and body composition, as well as quarterly eating behaviours, dietary intake, physical activity, sedentary behaviours, and basal metabolic rate changes amongst first-year Australian university students. Participants were first-year university students over 18 years. Results: Twenty-two first-year university students (5 males, 17 females) completed the study. Female students gained weight significantly at two, three and four-months (+0.9 kg; +1.5kg; +1.1 kg, p <0.05). Female waist circumference (2.5cm increase at two-months, p=0.012) and body fat also increased (+0.7%, p=0.04 at two-months; +0.9%, p=0.026 at three-months). Intake of sugar, saturated fat (both >10% of total energy) and sodium exceeded recommended levels (>2300 mg) at 12-months. Greater sedentary behaviours were observed amongst male students throughout the study (p <0.05). Conclusions: Female students are at risk of unfavourable changes in body composition during the first year of university, while males are at risk of increased sedentary behaviours. High intakes of saturated fat, sugars and sodium warrant future interventions in such a vulnerable group.