A substantial proportion of women who quit smoking during pregnancy will relapse in postpartum. In order to better understand the psychosocial factors which precipitate relapse to smoking we conducted a prospective study of postpartum smoking relapse among a cohort (N = 106) of women who quit smoking during pregnancy. Participants were surveyed by telephone after the 28th week of pregnancy, and at 6 weeks and 6 months postpartum. Point prevalence estimates of smoking relapse indicated that at 6 weeks and 6 months follow-up, 24% (n = 26) and 40% (n = 42), respectively, of the women had returned to regular smoking. Spouse's smoking status, social support, decreases in self-efficacy, and the types of coping strategies used to resist smoking in pregnancy and postpartum predicted relapse to smoking in postpartum. Longitudinal data indicated that relapse occurred relatively gradually suggesting that early postpartum is not too late to encourage new mothers to remain abstinent.