Adolescents engage in a complex range of low energy-consuming and active behaviours not easily captured by single behavioural measures. This study aims to describe the associations among adolescent active and low energy behaviours. Data were obtained from adolescents aged 12–16 years (n = 1532) participating in a nationally representative survey. Thirty-nine variables measuring activities were stratified by sex and age and then analysed using principal components analysis with Varimax rotation. Four components were derived for younger girls (21.7% of the variance) and younger boys (20.2%), six for older girls (29.7%) and five for older boys (25.6%). Academic-related behaviours positively correlated with each other and negatively with television use for all age–sex groups. Computer use correlated positively with academic-related behaviours for older boys but negatively with active behaviours for younger boys and girls. Active behaviours correlated positively with each other. For older girls, low energy expenditure, household-based behaviours were negatively correlated with active behaviours. Computer use appears to differ across age groups, and leisure and academic use should be differentiated. The positive associations among different active behaviours and their negative associations with home-based, low energy expenditure behaviours are of interest for intervention development.