Abstract Infants admitted to a neonatal unit (NNU) are frequently unable to feed by breast or bottle because of ill health or prematurity. These infants require nutritional support until they can start oral feeding. Breastfeeding is advocated for these infants, and mothers are frequently encouraged to express breast milk to be fed via the enteral tube. However, by discharge, breastfeeding rates tend to be low. Oral feeding requires careful management, and although practices may vary because of clinical need, some may be informed by unit norms. There is limited evidence for effective breastfeeding support in this environment and little exploration of the effect of routine feeding decisions. This study aimed to explore feeding decisions and considered how these might affect outcomes. The staff in the two large urban NNUs who participated in the feeding decisions were interviewed and the data were analysed using a theoretical framework. Feeding decisions were made mainly by the unit staff, with limited parental involvement. Subsequent management varied, with differences being related to staff experience and beliefs, unit norms, parent's expectations and physical constraints within the unit. The staff were overtly supportive of breastfeeding, but the need to monitor and quantify milk intake may undermine breastfeeding. Furthermore, feeding breastfed infants during the mothers' absence was controversial and provoked debate. There is a need for clear guidelines and increased parental involvement in feeding decisions. Routine practices within the system may discourage mothers from initiating and persisting with breastfeeding. A change in unit culture is required to fully support the parent's feeding choices.