This randomized double-blind, placebo-controlled will determine the relative efficacy of standard versus extended transdermal nicotine (TN) therapy for smoking cessation. After completing the eligibility screening, 600 treatment-seeking smokers will be randomized to receive either standard treatment (ST) with TN (21mg x 8 weeks, placebo x 16 weeks) or extended treatment (ET) with TN (21mg x 24 weeks). All participants will receive behavioral counseling. The primary outcome will be biochemically verified abstinence from smoking at the end of treatment (week 24). Secondary outcomes include abstinence at week 28 (4 weeks after treatment is discontinued), and time to failure. We hypothesize that ET will produce significantly higher quit rates than ST; however, the benefit of ET will last only so long as treatment is continued. Support for this hypothesis would indicate that maintenance therapy with TN should be considered.