This study examined the effects of a smoking cessation intervention on stages of change in 349 low-income, pregnant women. At first prenatal visit, women were randomized into experimental or usual care condition and classified by stage of change: precontemplation, contemplation, preparation, or action. For each stage of change at the first prenatal visit, the stage distributions of the experimental and usual care groups were compared at the second and 36-week prenatal visits. Kruskal-Wallis tests revealed significant differences at the second visit in the stage distributions by condition for subjects who were initially in precontemplation or in preparation. In each case, a greater proportion of experimental than usual care subjects advanced through the stages. The shift was not maintained at the 36-week visit.