The aim of this study was to provide a current assessment of Australian secondary students' self-reported dietary, physical activity and sedentary behaviour. This study also examined the relationship between television viewing and students' dietary behaviour. Data are from a cross-sectional survey of 18 486 secondary students in 2005 from all Australian states except Western Australia. Participants reported their usual daily consumption (number of serves) of vegetables and fruit; their weekly consumption of unhealthy/non-core foods including fast food meals, snack foods and high-energy drinks; their engagement in moderate-vigorous physical activity over the previous week; and hours spent using electronic media for entertainment and doing homework on school days. The study found that 20% of students were meeting the daily requirement of four serves of vegetables, whereas 39% were eating the recommended three daily serves of fruit. Consumption of unhealthy/non-core foods was high, with 46% of students having fast food meals at least twice a week, 51% eating snack foods four or more times per week and 44% having high-energy drinks four or more times per week. Fourteen per cent of students engaged in recommended levels of physical activity and 29% engaged in recommended levels of sedentary behaviour. Age and gender differences occurred for most measures, and there were some socio-economic status differences. Heavier television use was associated with lower consumption of fruit and higher consumption of unhealthy/non-core foods. On the basis of the results of this study, it appears that a significant proportion of Australian secondary students fall short of current, national dietary and physical activity recommendations for teenagers. Continual monitoring of these behaviours is essential to help inform research and policy and identify where future efforts should be directed.