The many biological advantages of breast milk call for promoting breast-feeding. The extent to which separation of ill newborns from their mothers negatively influences breast-feeding is not known. By means of a written inquiry, we investigated the prevalence of exclusive, partial, and no breast-feeding of 536 newborns hospitalized at a tertiary care neonatal center with no inborn patients. Three hundred twenty-seven questionnaires were completed correctly. Fifty percent of the mothers eventually succeeded in exclusive breast-feeding, 25% in partial breast-feeding, and 25% never breast-fed. The frequency of breast-feeding was similar to the Swiss average for the first 4 months of life in healthy newborns and declined more rapidly thereafter. Univariate and multivariate statistical analyses have shown that the following conditions influence breast-feeding negatively: gestational age ≤33 weeks, maternal age >25 years, and lower professional status of the father. Additionally, multivariate analysis revealed a promoting effect of previous breast-feeding. Exclusive breast-feeding has eventually been possible in half of the newborns who had initially been separated from their mothers due to illness. Knowledge of the conditions influencing breast-feeding in such populations should help to promote breast-feeding more specifically in tertiary neonatal centers.