BACKGROUND Recent increases in obesity prevalence have led to research into the neighbourhood food environment. Research suggests that proximity and density of food outlets around the home is associated with childhood obesity prevalence, however, the evidence is inconclusive, and associations between food outlet locations and diet are less clear. The purpose of this study is to assess area level associations between sales of unhealthy foods in supermarkets and weight status of children. METHODS This study examined the association between weight status in children (4-5 year olds and 10-11 year olds) measured in the National Child Measurement Programme over three time points (2008/9, 2009/10, 2010/11) and annual sales of unhealthy foods (2012/3), as identified from a large supermarket chain. Geographical analysis was conducted to link store-based food sales for 537 stores with 6517 UK Census Areas. Unadjusted associations were examined with error-bar plots and linear regression was used to examine the relationship between the prevalence of overweight and obesity and sales of unhealthy food, while controlling for covariates known to predict weight status in children. RESULTS A statistically significant relationship was identified between the sales of unhealthy foods and the prevalence of overweight and obese children in both age groups (p < 0.01). Of the covariates, area deprivation was positively associated with weight status (p < 0.001). Non-white population (%) was negatively associated (p < 0.001) with overweight and obesity among Reception children, but positively associated with the other weight statuses (p < 0.001). A higher proportion of children in the same age group were associated with statistically significantly lower overweight and obesity prevalence in Reception (p <0.01) but not Year 6 children. CONCLUSIONS The study provides novel findings linking supermarket food sales with the weight status of children. Food sales in geographically referenced supermarkets are a valuable source of data for research into the factors that influence the weight of the surrounding population. Future research could identify factors that might modify food shopping in supermarkets and use of purchasing data could be an effective way to measure the impact of healthy eating campaigns on the weight status of children over time.