OBJECTIVE To evaluate the growth of exclusively breastfed infants from birth to 6 months of life. METHODS This was a longitudinal study of 184 children who received primary care at a public institution (Exclusive Breastfeeding Stimulation Program, PROAME) in Belém, state of Pará, Brazil, between February 2000 and January 2001. A total of 102 children completed the study. All were born at full term with a birth weight greater than or equal to 2,500 g. No events were recorded during the neonatal period and the infants were exclusively breastfed, on demand, since their birth. The infants were followed up monthly, and the weight and length measured at birth and at the end of the first, fourth and sixth months of life were compared to the 50th percentile line of the NCHS growth charts and to other previous studies of Brazilian children who were exclusively breastfed. RESULTS Growth was adequate for all the children, who doubled their weight before the fourth month of life. Despite a slow-down in weight and height gain after the fourth month, the weight averages at 6 months were greater than the standards used for comparison. CONCLUSIONS The average weight of these exclusively breastfed children was above the 50th percentile of the NCHS curve at 6 months, thus confirming the nutritional advantages of breast milk, especially when the mothers receive guidance regarding the appropriate techniques for breastfeeding.