This study evaluated the efficacy of prolonged administration (18 months) of a nicotine nasal spray in smoking cessation and attempted to characterize the pattern of use of the nasal spray with a specially developed electronic monitor in an effort to assess the factors associated with cessation success or failure. Study participants were 92 patients in a smoking cessation unit of a medical outpatient clinic in Switzerland. Participants were daily smokers who had smoked for more than 5 years and were highly motivated to quit. The main outcome measure was the number of abstainers at 12 and 24 months. Their use of the spray was monitored using a microchip (MDILog) that recorded the date and time of every actuation. Success rates were 17.4% at 12 months and 9.8% at 24 months. During the first month of study, median use was 12 puffs/day in abstainers and 6 puffs/day in failures (p=.049). Abstainers used the spray less in the morning compared with failures (26.6% vs. 32.8% of the total median daily dose; p=.028). By contrast, abstainers used the spray more in the evening/night compared with failures (35.3% vs. 26.7% of the total median daily dose; p=.007). Abstinence during the first two weeks was associated significantly with cessation success at 6 months (OR=17.10) and 24 months (OR=11.09). Although the pattern of use of the nasal spray differed between successful quitters and failures (used in higher doses by the successful quitters), mean daily consumption during the first month was not predictive of success. Mean daily consumption of the nicotine nasal spray remained lower than expected in most participants, particularly in failures.