This study examined the pattern of activity energy expenditure (AEE) among New South Wales (NSW) high school students in relation to age, sex, socioeconomic status (SES), place of residence, cultural background, season, participation in moderate- and vigorous-intensity and in organized and non-organized physical activity. Methods: Cross-sectional survey of a randomly-selected sample (N = 2026). Respondents self-reported their physical activity participation during a usual week in summer and winter. Results: Boys reported greater AEE than girls and, whereas AEE was greater among grade 10 than grade 8 boys, the reverse was true for girls. Boys reported the same AEE for summer and winter, but girls reported less AEE during winter. Both boys and girls reported spending the same proportion of their AEE in vigorous-intensity (72%) compared with moderate-intensity activity (28%) and in non-organized (60%) compared with organized activity. There was no clear association between urban/rural place of residence and AEE. Although AEE tended to be positively associated with SES among girls, there was no association among boys. Girls from Asian cultural backgrounds reported much lower AEE than girls from other cultural backgrounds. Conclusion: Patterns of energy expenditure among adolescent boys and girls should be considered in developing interventions to ensure needs are adequately met.