Approximately 25% of children in Australia are obese or overweight; this can have implications for physical and psychological health. Research from Australia and other high-income nations has identified demographic and socio-economic factors which may be associated with children being overweight or obese; potentially modifiable aspects of nutrition and physical activity may also contribute. The aim of this study was to identify socio-demographic and behavioural factors associated with being overweight or obese in a sample of children aged 5 to 17 in Victoria, Australia. Data were collected by structured computer-assisted telephone interviews with parents of children aged 5-13 and adolescents aged 14-17 years. Obese or overweight was classified using International Obesity Taskforce (IOTF) age and sex-specific cut-off points for Body Mass Index. Analyses included data for 1,855 children from 23 Local Government Areas. The odds of being classified as overweight or obese were significantly higher for children aged 5-9 compared with children aged 14 - 17 (Adj O.R. = 2.041) and children who did not participate in at least one hour per day of physical activity (Adj O.R. = 1.679). Children who reported that they did not consume any soft drink in the past 2 weeks had significantly reduced odds (Adj O.R. = 0.688) of being classified as overweight or obese, compared with those who consumed any soft drink. Public health initiatives focused on developing children's knowledge, skills and physical literacy early in life should be complemented with whole-of-community approaches that support healthy food choices and encourage physical activity. Key Messages 1. Younger children (age 5 to 9) were most at risk of being overweight or obese. 2. Children who consumed sugar-sweetened soft drinks and who were not participating in sufficient daily physical activity were more likely to be overweight or obese. 3. Whole-of-community approaches may lead to reduction in the proportion of overweight and obese children, as some risk factors are potentially modifiable.