Objective: We used ecological momentary assessment to understand the physical activity and sedentary behaviour patterns of university students. Study design: Cross sectional, opportunistic sample from a university in the English midlands. Methods: Ecological momentary assessment diaries were completed every 15 minutes across two days. The sample comprised 46 males (mean age 20.2 years) and 38 females (mean age 19.5 years). The majority of participants were undergraduates (96.5 per cent) and white European (85 per cent). Results: Although "studying" was the predominant behaviour (280 minutes), students spent time conducting a range of behaviours including "watching television" (79.9 minutes), "sitting and talking" (72.1 minutes) and "hanging out" (64.0 minutes). Repeated measure ANOVAs revealed a significant gender effect for some behaviours with "studying" [F(1,82) = 10.50, p less than 0.006] and "computer game playing" [ F(1,82) = 7.97, p less than 0.006] being higher in males, and "sitting and talking" [F(1,82) = 24.49, p less than 0.006] higher in females. Pearson correlations suggested that sedentary behaviours compete with each other for students' time. A significant small negative relationship existed between sedentary technology behaviours and physical activity for males (r = -0.217) but not for females (r = -0.182). Conclusions: Students participate in a range of sedentary behaviours that differ by gender. Results question public perception that selected sedentary behaviours, such as "watching television", are responsible for declining levels of sport and exercise participation in this age group. Implications for interventions are considered. (Contains 2 tables.)