BACKGROUND: There are no randomized trials examining whether intensive advice to pregnant smokers is more stressful than standard care. METHOD: Nine hundred eighteen U.K. women currently smoking on commencing antenatal care were randomized into three arms. Women in Arm A received one episode of brief advice to stop smoking. Women in Arm B were assessed for stage of change and worked through an exercise in self-help manuals on three occasions. Women in Arm C used a 20-min interactive computer program three times in addition to the intervention women in Arm B received. Stress was assessed by the change in score on the Perceived Stress Scale (PSS) from baseline to 30 weeks gestation, the month before delivery, and 10 days postpartum. RESULTS: There were small and not significant differences in the changes in PSS between the arms at all outcome times. There was no evidence that the importance women attached to pleasing their midwife by stopping, having failed to quit, or nulliparity modified the effect of intensive advice on change in stress levels. CONCLUSIONS.: Intensive advice to stop smoking was not associated with increases in stress. Advice and support for pregnant women to stop smoking should be given without fear of causing stress.