Abstract Objective The aim of the present study was to explore the existence of clusters in multiple lifestyle behaviours, including physical activity (PA), sedentariness and food habits, in young adolescents. The present study also investigated whether the identified groups could be characterised by gender and components of health-related physical fitness, especially weight status and cardiorespiratory fitness (CRF). Design A cross-sectional survey. Leisure-time PA, sedentary behaviour and food consumption were assessed by a questionnaire. Overweight prevalence was estimated using BMI (kg/m 2 ) calculated from self-reported height and weight. CRF was measured using a 20 m shuttle-run test. Setting The study was conducted in four middle schools in Flanders, Belgium. Subjects The sample size was 317 seventh grade students aged 11–12 years. Results Four reliable and meaningful lifestyle clusters could be identified, labelled as ‘Sporty media-oriented mixed eaters’ (boys: n 34; girls: n 16), ‘Academic healthy eaters’ (boys: n 30; girls: n 58), ‘Inactive healthy eaters’ (boys: n 38; girls: n 57) and ‘Inactive media-oriented unhealthy eaters’ (boys: n 35; girls: n 49). The lifestyle clusters could not be characterised by adolescents’ weight status. Among boys, the ‘Sporty media-oriented mixed eaters’ group performed significantly better on the shuttle-run test than those in clusters with the lowest levels of PA (clusters 3 and 4). Conclusions Our results showed that healthy and risk-related behaviours may coexist in some groups of young adolescents. Isolated unhealthy behaviours, such as high levels of screen-based media use or high consumption of energy-dense food items, are not necessarily related with negative health outcomes, on the condition that these risk-related behaviours co-occur with more health-enhancing behaviours such as PA.