A retrospective cohort study on ECC and associated factors was conducted among mothers with 25- to 30-month-old infants in a community where prolonged breastfeeding was common practice. All infants who consumed sugary supplementary food or rice that was pre-chewed by the mother, or who fell asleep with the breast nipple in their mouths, had ECC. Infants without those habits, and who were breastfed up to 12 months, had no ECC. Breastfeeding during the day beyond the age of 12 months was not associated with ECC, but infants who were breastfed at night > 2 times had an OR for ECC of 35 (CI 6-186), and those who were exposed to > 15 min per nocturnal feeding had an OR for ECC of 100 (CI 10-995). The present study indicates that, in this population, besides the consumption of sugars and pre-chewed rice, nocturnal breastfeeding after the age of 12 months poses a risk of developing ECC.