In a prospective study, feeding routines of a maternity unit and the subsequent feeding patterns of 521 newborns were analysed. During the stay in the maternity unit, 69% of newborns were exclusively breast fed and 1% received only donor's milk from the milk bank and/or formula. Nine percent received their mothers' milk by bottle at least once and 21% received one or more supplementary feedings with donor's milk from the milk bank. One‐quarter of the children received supplementary feeds on the third day of life, the indications for this being birth weight less than 3.0 kg, maternal diabetes or gestational diabetes, “insufficient amounts” of milk or fussiness. At three months, 65% were being exclusively breast fed and 15% partially breast fed. In a multiple logistic regression analysis, the potential determinants (neonatal feeding, maternal characteristics, characteristics of the delivery and the child) for the duration of breast feeding were included. The adjusted relative risk (estimated as odds ratios, OR) of not being breast fed at three months was associated with maternal age (<25 years, OR 4.2), maternal smoking (OR 4.0), neonatal feeding (supplements given, OR 3.9) and initial weight loss (10% or more, OR 2.8). Thus the administration of supplementary donor's milk or formula during the early neonatal period was associated with an increased risk of a short duration for breast feeding, even after adjustment for a number of potential confou