Motivational interviewing is a technique used to promote change in addictive behaviour, initially used to treat alcoholism. Despite this, its effectiveness has not been sufficiently demonstrated for giving up smoking. The aim of the study was to establish whether motivational interviewing, compared with anti-smoking advice, is more effective for giving up the habit. Randomised controlled trial. Primary care in Albecete, Spain. Random experimental study of 200 smokers assigned to two types of interventions: anti-smoking advice (n = 86) and motivational interviewing (n = 114). Subjects in both groups were offered bupropion when nicotine dependency was high (Fagerström score >7). The success rate was evaluated by intention to treat; point prevalence abstinence was measured 6 and 12 months post intervention by personal testimony, confirmed by means of CO-oximetry (value < 6ppm). The measure of effectiveness of the treatment for giving up smoking after both 6 and 12 months, showed that the motivational interviewing action was 5.2 times higher than anti-smoking advice (18.4 % compared to 3.4%; 95% confidence interval = 1.63 to 17.13). The results of our study show that motivational interviewing is more effective than brief advice for giving up smoking.