Breast-fed infants suffer more weight loss and breast milk volume is insufficient during the early days of life. Does this cause hypoglycemia? We examined the incidence of hypoglycemia (< 40mg/dL), factors contributing to the prevention of hypoglycemia and how the mode of delivery effects blood glucose levels during the first 72 hours of life. We studied neonates who were: 1) healthy, term infants born at our hospital; 2) breast fed within 30 minutes of birth; 3) birthweight > 2500g; 4) gestational age > 37wks; 5) Apgar > 7 at 1 min. Rooming-in starts immediately after birth for vaginally born infants and at 48-72 hours for C-section babies. The times and frequency of breast feeding are not predetermined. Blood glucose levels were measured randomly by Antsenese with 5ul of whole blood. Infants born by C-section (n = 11) lost significantly more weight and received 5% glucose supplements significantly more often than those born vaginally (n = 30). Vaginally delivered babies regained birthweight more rapidly than those born by C-section. The frequency of breast-feeding increased significantly from birth to 13 times/24 hours on day 2 in infants born vaginally (significantly higher than that of infants delivered by C-section during the first 5 days of life). Feeding frequency in C-section infants did not increase rapidly even if rooming-in started after 48-72 hours of life. Blood glucose levels were significantly lower in infants delivered by C-section during 36-72 hours of life compared with infants born vaginally (52.3±9.1 vs 69.2±10.9mg/dL p < 0.01). However, symptomatic hypoglycemia did not occur in either group. Our results suggest that hypoglycemia (< 40mg/dL) seldom occurs in healthy, full term, breast fed neonates when they are cared for by rooming-in immediately after birth. Early and frequent suckling is necessary for the prevention of hypoglycemia in breast fed neonates. Infants born by C-section should have their blood glucose levels monitored because feeding behavior is different from infants born vaginally.