Introduction: There is increasing evidence that a high proportion (47%–63%) of women who quit smoking during pregnancy relapse during the postpartum period. The purpose of this population-based study was to examine the association between selected sociodemographic factors and smoking relapse in the early postpartum period (within the first 6 weeks) in women who had successfully quit smoking during the pregnancy. Methods: The study included 512 women resident in East Sussex, United Kingdom, who had quit smoking during the pregnancy. Information on the prevalence of smoking and selected sociodemographic factors and breast feeding at the 6-weeks postpartum review by health visitor was obtained from the Child Health Surveillance System, which records and monitors the health and development of children from birth until school entry. Results: Of the 512 women who had quit smoking during the pregnancy, 238 (46.5%) relapsed in the early postpartum period. In the bivariate analysis, there was an association between deprivation and smoking relapse in the early postpartum period(OR = 5.3, 95% CI: 2.5–11.4), with a significant trend in increasing risk of relapse with increasing level of deprivation (p < .01). Stepwise logistic regression analysis showed that women who lived in deprived urban areas (OR = 2.3, 95% CI: 1.2–4.2), had =3 children (OR = 3.8, 95% CI: 2.2–6.4), and had other smokers in the household (OR = 5.6, 95% CI: 3.6–8.8) were significantly more likely to relapse in the early postpartum period. On the other hand, women who were breast feeding were significantly less likely to relapse (OR = 0.6, 95% CI: 0.4–0.9). Conclusions: Factors associated with early postpartum smoking relapse identified in this study, particularly breast feeding, high parity, and concurrent smoking by partner/other household member(s), may contribute to the development of effective and targeted interventions to maintain smoking cessation in women and their household.