This study examined the long-term effectiveness of a postpartum smoking relapse prevention intervention by evaluating the smoking status and smoking cessation self-efficacy of original study participants at 12 months following delivery. Two hundred and thirty-eight women who had participated in a randomized clinical trial, a nurse-delivered relapse prevention intervention, were visited in their homes. Data were collected on smoking status, self-efficacy, mental health, alcohol use, breast feeding, social support, smoking in the social environment, and sociodemographics. Smoking status was verified with measures of carbon monoxide in expired air. The 12-month continuous smoking abstinence rate was 21.0% in the treatment group and 18.5% in the control group; odds ratio (OR) = 1.17, 95% confidence interval (CI) = 0.62-2.22. One half (50.4%) of the control group and 41.2% of the treatment group reported smoking daily at 12 months; OR = 1.45, 95% CI = 0.87-2.43. The treatment group attained higher self-efficacy. Four variables were associated with relapse to daily smoking; breast feeding and mental health had protective effects, while partners who smoked and greater amount smoked prior to pregnancy had adverse effects.