Objective To identify current prevalence and sociodemographic distribution of adherence to national diet and physical activity and sedentary behaviour guidelines among Australian primary school children. Study design Cross-sectional survey of children (n = 4637, 9–11 years) participating at baseline in the South Australian Obesity Prevention and Lifestyle (OPAL) programme evaluation. Methods Self-reported diet, physical activity (PA) and screen time (ST) behaviours were assessed via questionnaire. Children were classified as meeting or not meeting each guideline (two or more serves of fruit, five or more serves of vegetables, two or less serves of discretionary food, ≥60 min of PA, and ≤2 h of ST per day). Results Although 65% of children met fruit recommendations, only 22% met vegetable recommendations (17% consumed no vegetables). Approximately one-quarter (28%) of children met discretionary food recommendations. Only 17% of children met the ST recommendations and 33% met PA recommendations. Less than 1% of children met all five recommendations. Rural children were more likely to meet both PA (OR = 1.45, 95% CI: 1.21–1.74, P < 0.001) and ST (OR = 1.37, 95% CI: 1.14–1.66, P < 0.01) recommendations than urban counterparts. Children at least socio-economic disadvantage performed better than those at greatest disadvantage for most behaviours. Conclusion Improvement in Australian children's diet and physical activity and sedentary behaviours, particularly urban children and those at greatest socio-economic disadvantage, is urgently warranted.