The aim of the current study was to examine whether parental mental health, parent-infant relationship, infant characteristics and couple's relationship factors were associated with the infant's development. Forty-two families took part at three time points. The first, at 3?months postpartum, involved a video recorded observation (CARE-index) of parent-infant interactions. At 5?months postpartum, in-depth clinical interviews (the Birmingham Interview of Maternal Mental Health) assessed parental mental health and parental perceptions of their relationship with their infant, their partner and their infant's characteristics. Finally, the Bayley Scales III was carried out 17?months postpartum to assess the infants' cognitive, language and motor development. A higher mother-infant relationship quality was significantly associated with more optimal language development, whilst a higher father-infant relationship quality was associated with more advanced motor development. Additionally, maternal postnatal post-traumatic stress disorder had a negative impact on the infant's cognitive development, whilst maternal prenatal depression was associated with a less optimal infant's language development. The largest prediction was afforded by parental perceptions of their infant's characteristics. The findings indicate that such perceptions may be crucial for the infant's development and imply that negative internal parental perceptions should be considered when assessing risk factors or designing interventions to prevent negative child outcomes.