Objective: To explore young adult's experiences of how starting university influenced their physical activity, diet, sleep, and mental well-being, and barriers and enablers to health behavior change. Participants: University students aged 18-25 years. Methods: Three focus groups were conducted in November 2019. Inductive thematic approach was utilized to identify themes. Results: Students (female: n = 13, male: n = 2, other gender identity: n = 1, 21.2 (1.6) years) reported mental well-being, physical activity levels, diet quality and sleep health were negatively affected. Stress, study demands, university timetabling, not prioritizing physical activity, cost and availability of healthy foods, and difficulty falling asleep were key barriers. Health behavior change interventions aiming to support mental well-being need to include both information and support features. Conclusions: There is a significant opportunity to improve the transition to university for young adults. Findings highlight areas to target in future interventions to improve physical activity, diet, and sleep of university students.