Objectives. This study is an evaluation of relapse prevention interventions for smokers who quit during pregnancy. Methods. Pregnant smokers at 2 managed care organizations were randomized to receive a self- help booklet only, prepartum relapse prevention, or prepartum and postpartum relapse prevention. Follow-up surveys were conducted at 28 weeks of pregnancy and at 8 weeks, 6 months, and 12 months postpartum. Results. The pre/post intervention delayed but did not prevent postpartum relapse to smoking. Prevalent abstinence was significantly greater for the pre/post intervention group than for the other groups at 8 weeks (booklet group, 30%; prepartum group, 35%; pre/post group, 39%; P = .02 [different superscripts denote differences at P < .05]) and at 6 months (booklet group, 26%; prepartum group, 24%; pre/post group, 33%; P = .04) postpartum. A nonsignificant reduction in relapse among the pre/post group contributed to differences in prevalent abstinence. There was no difference between the groups in prevalent abstinence at 12 months postpartum. Conclusions. Relapse prevention interventions may need to be increased in duration and potency to prevent postpartum relapse.