Postpartum relapse is common among women who stop smoking during pregnancy. We examined predictors of postpartum relapse in 87 women who quit smoking during pregnancy, 48% of whom relapsed by 6 months postpartum. We also explored the circumstances surrounding their first postpartum cigarette. Multivariate analyses revealed that having more friends/family members who smoke, smoking more heavily pre-pregnancy, and having higher depression scores and less concern about weight at the end of pregnancy were associated with increased risk of relapse postpartum. Most women's first postpartum cigarettes were unplanned, in the presence of another smoker, and while experiencing negative affect. The findings suggest targets for interventions to reduce postpartum relapse.