INTRODUCTION: Both SES and supermarket choice have been associated with diet quality. This study aimed to assess the contributions of supermarket choice and shopping behaviors to the healthfulness of purchases and social patterning in purchases. METHODS: Observational panel data on purchases of fruit and vegetables and less-healthy foods/beverages from 2010 were obtained for 24,879 households, stratified by occupational social class (analyzed in 2014). Households' supermarket choice was determined by whether they ever visited market-defined high- or low-price supermarkets. Analyses also explored extent of use within supermarket choice groups. Shopping behaviors included trip frequency, trip size, and number of store chains visited. RESULTS: Households using low-price (and not high-price) supermarkets purchased significantly lower percentages of energy from fruit and vegetables and higher percentages of energy from less-healthy foods/beverages than households using high-price (and not low-price) supermarkets. When controlling for SES and shopping behaviors, the effect of supermarket choice was reduced but remained significant for both fruit and vegetables and less-healthy foods/beverages. The extent of use of low- or high-price supermarkets had limited effects on outcomes. More-frequent trips and fewer small trips were associated with healthier purchasing for both outcomes; visiting more store chains was associated with higher percentages of energy from fruit and vegetables. CONCLUSIONS: Although both supermarket choice and shopping behaviors are associated with healthfulness of purchases, neither appears to contribute to socioeconomic differences. Moreover, differences between supermarket environments may not be primary drivers of the relationship between supermarket choice and healthfulness of purchases.