Postnatal depression is a psychological disorder which occurs within six weeks after childbirth. It is a serious mental health problem for women and its consequences have important implications for the welfare of the family and the development of the child. Postnatal depression is a recognised cause of delayed cognitive development in infants in developed countries. This research aims to determine whether postnatal depression contributes to poor growth and development outcomes in Goa, India. Key messages of the research include: postnatal depression may be a cause of poor growth outcomes in infants at six months in South Asia – this study has reported a strong association after adjustment for a number of possible confounders, but cannot rule out the role of an unmeasured variable; postnatal depression is associated with significantly poorer achievements of mental development in infants at 6 months; this study provides evidence for a new, potentially treatable, cause for poor infant growth outcomes from a region which has the highest poor growth outcomes rates in the world; and assessment and management of postnatal depression must be an integral part of antenatal and infant clinics in South Asia