Data from the Oklahoma Pregnancy Risk Assessment Monitoring System (PRAMS) were assessed to determine the prevalence of maternal cigarette smoking and its relationship to pregnancy outcomes. A mail and telephone questionnaire was used to survey mothers between four and six months postpartum to obtain information about smoking and other maternal behaviors. Monthly samples were drawn from the state's live birth registry utilizing a systematic stratified sampling approach based on infant birth weight. A total of 3,051 responses were received between 1988 and 1990 for an overall return rate of 70%. Results of the study show approximately one-third (32%) of women in Oklahoma smoked 3 months prior to pregnancy, 22% smoked in their last 3 months of pregnancy, and 29% smoked shortly after delivery. Women who smoked during pregnancy were 2.2 times more likely to deliver a low birth weight (LBW) infant than nonsmokers, and 1.4 times more likely to have gained less than the recommended amount of weight. Additionally, women who smoked during pregnancy were 1.4 times more likely to begin prenatal care in the second or third trimester, or to receive no care at all. In conclusion, maternal smoking cessation has the potential for dramatically reducing preventable adverse outcomes of pregnancy.