A study evaluated the effectiveness of general practitioners' (GPs) advice against smoking. Over 2138 cigarette smokers in London were divided into four groups. Group 1 received no intervention, group 2 received only a questionnaire, group 3 received advice to stop smoking, and group 4 received advice, a leaflet, and a follow-up warning. Follow-up data were collected at one month and one year. At one month, 88% of patients provided data, and at one year, 73%. Immediate advice increased motivation and intention to stop smoking. Most smokers who stopped did so due to the advice, which motivated more people to try quitting rather than increasing success rates. The effect was strongest in the first month but persisted for three months. The leaflet and follow-up warning enhanced the short-term effect. Long-term, the relapse rate was lower in those who stopped, but this was not enhanced by the leaflet or follow-up. The proportions of smokers who stopped and remained smoke-free after one year were 0.3%, 1.6%, 3.3%, and 5.1% in groups 1-4, respectively. The results suggest that if all GPs in the UK adopted this approach, over half a million ex-smokers could be achieved annually. This is more effective than current withdrawal clinics. The study highlights the potential of GPs to significantly reduce smoking rates through simple, routine advice.A study evaluated the effectiveness of general practitioners' (GPs) advice against smoking. Over 2138 cigarette smokers in London were divided into four groups. Group 1 received no intervention, group 2 received only a questionnaire, group 3 received advice to stop smoking, and group 4 received advice, a leaflet, and a follow-up warning. Follow-up data were collected at one month and one year. At one month, 88% of patients provided data, and at one year, 73%. Immediate advice increased motivation and intention to stop smoking. Most smokers who stopped did so due to the advice, which motivated more people to try quitting rather than increasing success rates. The effect was strongest in the first month but persisted for three months. The leaflet and follow-up warning enhanced the short-term effect. Long-term, the relapse rate was lower in those who stopped, but this was not enhanced by the leaflet or follow-up. The proportions of smokers who stopped and remained smoke-free after one year were 0.3%, 1.6%, 3.3%, and 5.1% in groups 1-4, respectively. The results suggest that if all GPs in the UK adopted this approach, over half a million ex-smokers could be achieved annually. This is more effective than current withdrawal clinics. The study highlights the potential of GPs to significantly reduce smoking rates through simple, routine advice.