The establishment of a good relationship between the parents and their new baby is one of the crucial factors in enhancing the outcome of postnatal care. The objective of this study was to assess the value and meaning of a descriptive list of baby adjectives, as a tool in the measurement of this relationship, for use in research aimed at improving postnatal outcomes. The list was used in a prospective longitudinal questionnaire survey of postnatal care. The adjectives allowed parents to express negative as well as positive feelings about their child. A score derived from the adjectives was explored using multiple regression to identify significant associations with other factors. The net adjective score proved a responsive and time-sensitive method for tracking changes in parental perceptions of their baby over time. Mothers' scores became more positive within the first two months with little change thereafter, and were more positive than fathers at 12–18 months. Mothers' scores were related to maternal anxiety and depression, and aspects of baby behaviour such as sleeping and crying problems, colic and teething; but not to obstetric factors such as method of delivery. Fathers' scores were affected by their partners' adaptation to motherhood and the baby's behaviour. The net adjective score is a useful and simple method of accessing parental perceptions of their babies. It could be used as an outcome measure in trials of interventions to improve postnatal outcomes.