Research linking postpartum depression (PPD) with negative child outcomes has predominantly examined PPD at six weeks postpartum or later, and has not controlled for depression during pregnancy. The present study examined associations between PPD at three weeks postpartum and temperament in 6-month-old infants in a sample of women who were not depressed during pregnancy. Depression was assessed at three weeks and six months postpartum using the Postpartum Depression Screening Scale (PDSS). Observed and maternal report of infant temperament was assessed when infants were 6-months-old. PPD symptoms significantly predicted observed temperament behaviour and explained maternal report of infant temperament. Symptoms of PPD at three weeks postpartum were a stronger predictor than at six months. Findings suggest that early depressive symptoms may be particularly problematic, and have implications for early assessment and treatment of PPD even in women who were not depressed during pregnancy or are otherwise considered low risk.