Sedentary behaviour is becoming a popular area of health research, but most studies report data on samples from Australia, the UK and USA, and on a narrow range of behaviours. The present study reports on the prevalence of multiple sedentary behaviours in a sample of secondary school students (n = 635; mean age 16.0 years) from Romania and Slovakia. Ecological Momentary Assessment diaries were used to record multiple behaviours across weekdays and weekend days. Results showed high levels of many sedentary behaviours, particularly for screen time at weekends. Other behaviours included homework, sedentary socializing and motorized transport. Gender, age and country differences were evident for some behaviours. Interventions may need to account for socio-demographic moderators, and studies need to assess multiple sedentary behaviours. (Contains 9 tables.)