This paper describes a rapid assessment of current infant feeding practices conducted during a mass immunization campaign in an urban area of São José do Rio Preto, São Paulo State, Brazil. Parents or guardians of all infants (<1 year) attending the 8 randomly-selected health centers were interviewed. Median duration of breastfeeding practices was estimated by probit analysis. Of the 719 infants, 692 (96.2%) began breastfeeding, and only 63 (8.9%) were in exclusive breastfeeding. Median duration of total breastfeeding (exclusive plus partial) was 205.93 days. Infants born by cesarean section showed a higher risk of early weaning: OR (95%CI)=1.51 (1.09-2.09) after adjusting for confounding variables (mother's educational level, gestational age, birth weight, whether breastfed). Median duration of total breastfeeding was higher among infants born by vaginal delivery (227.38 days; 95%CI=195.19-271.16) as compared to cesarean section (192.84 days; 95%CI=128.23-273.34). Early introduction of weaning foods such as water/herbal tea and cow's milk was observed with a median age at introduction of 30 days. These findings indicate the need to improve strategies by the public health services to promote exclusive breastfeeding.