This article evaluates the relationship of social support to smoking cessation and continued abstinence of 3923 men and women with mild to moderate airway obstruction in the Lung Health Study. At both the end of a 12-week group program and after 1 year, men but not women who were supported in quitting were more likely to be successful. Married status facilitated quitting but was less strongly related to long-term abstinence. Participants supported by an ex-smoker who had attended the group program with them were very likely not smoking after 1 year (men, 74.7%; women, 72.4%). Participants supported by a smoker were less than half as likely to have achieved abstinence after 1 year but still had cessation rates greater than 30%. The nature of these relationships has implications for the distinction between women and men in studies of social support and for intervention strategies. Support people should be included in cessation intervention programs. Spouse involvement, however, is more evidently useful for men than for women.