We studied the relationship between rooming-in/not rooming-in and breast-feeding variables such as breast feeding frequency, breast milk intake, supplements of other human milk or 5% glucose solution, cumulative weight loss, weight recovery and hyperbilirubinemia. We found that the breast feeding frequency was significantly higher in infants rooming-in than in those not rooming-in. Intake of breast milk on days 3 and 5 was significantly lower and maximum weight loss was significantly higher in infants rooming-in than in those not rooming-in. Infants rooming-in also had less supplement of other human milk compared with non-rooming-in infants (p less than 0.01). However, the weight increase per day from minimum to weight on day seven was higher in infants rooming-in than in non-rooming-in infants (39.3 +/- 21.4 g/day vs. 31.4 +/- 15.3 g/day, p less than 0.01). The frequent suckling by rooming-in infants may explain, in part, the better weight gain, since frequent suckling may decrease energy consumption by reducing movement and crying during the early days of life, thus contributing to better weight gain. Our study suggests that some of the neonatal feeding problems related to breast feeding could be eliminated by education of mothers and nurses and by changes in hospital policies and practices in breast feeding.