BackgroundFood marketing exposure has the potential to influence children’s dietary behaviours and health status, however, few studies have identified how ‘obesogenic’ the outdoor food marketing environment is along public transport (bus and/or train) or walking routes that children take to school.MethodsAudits of all outdoor advertisements present along likely train, bus and walking routes to 24 secondary schools (ie, 3 routes per school, 72 routes total) were conducted in Perth, Western Australia (WA). The size, content, type and setting of each advertisement were recorded in accordance with the International Network for Food and Obesity/non-communicable diseases Research, Monitoring and Action Support protocol for monitoring outdoor advertising.ResultsOf the 4016 total advertisements observed, almost half were for food (n=1754, 44%) and of these, 80% (n=1397) advertised discretionary (non-core) foods, and 8% (n=138) advertised healthy (core) foods. On average, commuting to school by train, bus and walking exposed Perth schoolchildren to 37.1, 22 and 4.5 discretionary (non-core) food ads per one-way trip to school, respectively.ConclusionsChildren living in Perth, WA experience a high level of exposure to unhealthy outdoor food advertisements during the school commute. Policies which restrict the placement and content of outdoor advertising, could be a useful strategy in the fight against childhood obesity.