BACKGROUND: A partner's provision of support and smoking status has been consistently associated with women's likelihood of smoking cessation during pregnancy and relapse in postpartum. DESIGN: A three-group randomized controlled intervention trial was conducted in 1996 to 2001, with 583 women and their partners randomized to usual care (UC), woman-only (WO), or partner-assisted (PA) intervention. Follow-ups occurred at 28 weeks of pregnancy, and 2-, 6-, and 12-months postpartum. SETTING: Womack Army Medical Center (WAMC) at Fort Bragg in Fayetteville, North Carolina. INTERVENTION: Women in the UC condition received provider advice to quit and a self-help guide. The WO condition received UC components plus a late-pregnancy relapse prevention kit (booklet and gift items) and six counseling calls (three in pregnancy and three postpartum) initiated by a health advisor. Women in the PA condition received the WO intervention, and their partners received telephone counseling and a support guide emphasizing skills to help the woman build and maintain her confidence to quit smoking. Partners who smoked also received cessation aids and related counseling. MAIN OUTCOME MEASURE: Seven-day self-reported abstinence from smoking at each follow-up. RESULTS: Intent-to-treat analyses showed no significant differences by condition in women's reports of abstinence at any follow-up. In late pregnancy, more partners were abstinent in the PA condition (15%) than in the UC condition (5%), p =0.02. CONCLUSIONS: Partner-assisted smoking-cessation interventions need further refinement. Influencing young couples' support patterns may require more intensive and conjoint intervention. Partners who smoke could benefit from support for their cessation efforts.