This study examined the association between prenatal exposure to cigarettes and infant and maternal negative affect. Participants were 115 mother-infant dyads (69 prenatally exposed to cigarettes and 46 nonexposed). Infant and maternal negative affect were both assessed during the neonatal period (2-4 weeks of age) and again at 7 months of infant age. Results indicated that only prenatal exposure to cigarettes predicted infant negative affect. Infants who were prenatally exposed to more cigarettes had higher levels of negative affect at both time points. Furthermore, regression analyses indicated that both infant and maternal negative affect during the neonatal period predicted maternal negative affect at 7 months of age. These results highlight the importance of considering the reciprocal relationship between infant and maternal behavior when examining developmental outcomes among infants prenatally exposed to cigarettes.