This study explored the manner in which bed-sharing is practised by breastfeeding infants in the UK, and examined how alternate definitions and interpretations of breastfeeding and bed-sharing can lead to confusion in understanding what bed-sharing entails. Longitudinal studies on parent-infant bed-sharing practices are scarce, but are vital to our understanding of normative bed-sharing behaviour. We gathered data using a longitudinal study of sleeping and feeding practices in England involving 97 initially breastfed infants from birth to 6 months of age whose behaviour was monitored weekly for a 6-month period. Results demonstrated that bed-sharing practices covary with breastfeeding practices, and that a single model of bed-sharing behaviour does not adequately reflect the experience of all infants. Our findings have ramifications for the way in which case-control studies address attempt to ‘measure’ bed-sharing, and our understanding and interpretation of bed-sharing risk factors.