The purpose of this study was to evaluate the demographic, socioeconomic, and lifestyle factors associated with quality of diet in adults residing in Greater Metropolitan São Paulo, Brazil. This was a cross-sectional, population-based study conducted in the district of Butantã and the municipalities of Itapecerica da Serra, Embu, and Taboão da Serra, based on data from a questionnaire and 24-hour recall from 1,840 adults, both males and females, included in a household health survey (ISA-SP). Dietary quality was assessed using the Healthy Eating Index (HEI) adapted to the local reality. Linear regression analysis was used to evaluate the relationship between HEI and other variables. Most individuals (75%) ate diets that were rated as "need improvement". The mean HEI was low for fruit, vegetables, and dairy products. Number of durable goods, head-of-family's schooling, and age >or= 60 years were associated with HEI in men. For women, age was associated with HEI. Energy intake was considered an adjustment variable for both genders.