A large body of literature has investigated the effects of postnatal depression on infant development. However, the particular circumstances in which depression is associated with adverse effects remain unresolved. Factors, such as the nature of depression (e.g., duration and severity) and the context with respect to other risk and protective factors (e.g., socioeconomic status and child gender) have been suggested as moderators of the effects of postnatal depression on infant outcomes. This study examined the impact of brief and chronic depression in a non-poverty sample of 112 mothers and their infants. Infant language development was assessed at 12 months, and at 15 months the Bayley Scales of Infant Development-II were administered. Chronic maternal depression, lasting throughout the first 12 months postpartum and beyond, was associated with lower infant cognitive and psychomotor development, with the effects being similar for boys and girls, while brief depression did not significantly impact the infant performance. Language development and infant behavior during testing were equivalent across the groups. The relatively high rates of motor development delay associated with chronic maternal depression found in this study are discussed along with the methodological issues and models of cumulative risk.