Maternal smoking during pregnancy has been consistently associated with aggressive behaviors among offspring across the life course. We posit that anger, as a precedent of aggression, may have mediated the association. The current study examines the relation between maternal smoking during pregnancy and anger proneness among the adult offspring. Participants were 611 adult offspring (ages 38-48 years) of mothers enrolled in the Collaborative Perinatal Project between 1959 and 1966 in Boston and Providence. Information on maternal smoking during pregnancy was collected during prenatal visits. Spielberger's trait anger scale was used to measure anger proneness which has two components: anger temperament and angry reaction. Results from the full sample analyses showed that offspring whose mother smoked one pack or more per day on average scored 1.7 higher in anger temperament T scores in comparison to offspring whose mother never smoked during pregnancy (β=1.7, 95% Confidence Interval (CI): 0.1, 3.2). The fixed effects analyses among siblings that accounted for more confounding found a greater effect of around one standard deviation increase in anger temperament T scores corresponding to maternal smoking of one pack or more (β=7.4, 95% CI: 0.5, 14.4). We did not observe an association of maternal smoking during pregnancy with offspring angry reaction or other negative emotions including anxiety and depression. We concluded that prenatal exposure to heavy cigarette smoke was associated with an increased level of anger temperament, a stable personality trait that may carry the influence of prenatal smoking through the life course.