We report patterns of prenatal smoking cessation and postpartum relapse for a large urban population of pregnant women. We examined associations between sociodemographic factors and prepregnancy, pregnancy, and early postpartum smoking behavior. Forty-one percent of women smoking before pregnancy quit smoking during pregnancy. Sociodemographic factors important in predicting smoking cessation during pregnancy, as determined through logistic regression analyses, differed significantly for white and black women. Among white women, education, age, and parity were important predictors of cessation, whereas among black women, only intention to breastfeed was a significant predictor of smoking cessation during pregnancy. Early postpartum smoking relapse rates differed by ethnicity. Twenty-eight percent of white women and 46% of black women who had quit during pregnancy relapsed within 6-12 weeks postpartum. Using logistic regression, we found formula feeding to be the most important predictor of early postpartum smoking relapse for both white and black women.