OBJECTIVE To evaluate the efficacy of the transdermal nicotine patch as an aid to smoking cessation when used as an adjunct to a cognitive-behavioural group intervention and to assess the effectiveness of the patch in ameliorating withdrawal symptoms. METHODS Double-blind placebo-controlled randomised trial with six months' follow-up of those who returned to the hospital-based outpatients smoking cessation clinic. METHODS Three hundred and thirteen smokers recruited from the local community. Mean age was 42 years, 48% were male, mean cigarette consumption was 29 per day and mean duration of smoking was 24 years. METHODS Cognitive-behavioural intervention delivered in a group context, two hours once a week over five weeks, self-help manual, and 24-hour daily nicotine patch treatment for 10 weeks. METHODS Point prevalence abstinence at three and six months, and sustained cessation from end of treatment to six months, with biochemical validation (expired carbon monoxide). We examined the effectiveness of the nicotine patch in ameliorating specific withdrawal symptoms by self-report of degree of severity. RESULTS The active nicotine patch resulted in significantly higher biochemically confirmed abstinence rates when compared with placebo at three months (48% v. 21%) and at six months (33% v. 14%). Six-months' continuous abstinence rates were also significantly higher among the active nicotine group (25%) compared with placebo (12%). The most common adverse events among active patch users were sleep disturbance and local skin irritation. The nicotine patch reduced the severity of some withdrawal symptoms. A low level of dependence was the strongest predictor of three and six months' abstinence. CONCLUSIONS The transdermal nicotine patch is effective when used as an adjunct to a group cognitive-behavioural intervention and it provides relief from withdrawal symptoms associated with nicotine dependence.