On average, the length of time women remain in hospital after giving birth in the UK has deceased in recent years but most women are nevertheless admitted to a postnatal ward after childbirth. In this unique, prospective, observational study, we drew upon the expertise of caregivers on postnatal wards to reveal a wide range of obstetric, medical, neonatal and social problems that can lead to prolonged hospital stay. A woman's stay was likely to be increased by the greatest amount if her baby required specialised care but bed occupancy was more strongly influenced by the presence of obstetric complications because these were common. In this paper, we describe inpatient postnatal activity in detail and make recommendations for the safe and effective development of postnatal services.