AbstractObjective:The present study describes the energy content of primary-school children’s lunchboxes and the proportion of lunchbox foods considered discretionary. Subgroup analyses by sex, socio-economic status, age and weight status were undertaken.Design:A cross-sectional study was conducted. Mean kilojoule content, number of items and categorisation of foods and drinks in lunchboxes as ‘everyday’ (healthy) or discretionary (sometimes) foods were assessed via a valid and reliable lunchbox observational audit.Setting:Twelve Catholic primary schools (Kindergarten–Grade 6) located in the Hunter region of New South Wales, Australia.Participants:Kindergarten to Grade 6 primary-school students.Results:In total, 2143 children (57 %) had parental consent to have their lunchboxes observed. School lunchboxes contained a mean of 2748 kJ, of which 61·2 % of energy was from foods consistent with the Australian Dietary Guidelines and 38·8 % of energy was discretionary foods. The proportion of lunchboxes containing only healthy foods was 12 %. Children in Kindergarten–Grade 2 packed more servings of ‘everyday’ foods (3·32 v. 2·98, P < 0·01) compared with children in Grades 3–6. Children in Grades 3–6 had a higher percentage of energy from discretionary foods (39·1 v. 33·8 %, P < 0·01) compared with children in Kindergarten–Grade 2 and children from the most socio-economically disadvantaged areas had significantly higher total kilojoules in the school lunchbox compared with the least disadvantaged students (2842 v. 2544 kJ, P = 0·03).Conclusions:Foods packed within school lunchboxes may contribute to energy imbalance. The development of school policies and population-based strategies to support parents overcome barriers to packing healthy lunchboxes are warranted.