The aim of this work was to study the prevalence of smoking in an urban population from cities with low environmental pollution. From a sampling of basic and high school children, 1959 subjects coming from 406 homes were selected for the study and answered a questionaire about smoking. The adjusted prevalence of smoking among subjects older than 10 years old was 36,5% and 40,8% in subjects older than 15 years old. Prevalence in males was 49,4% and 35% in female. However among subjects between 10 and 15 years old, females had a higher prevalence of smoking. Most subjects smoked 1 to 9 cigarettes/day, always aspirated smoke and consumed all the cigarette. The prevalence of passive smokers was 65,5%. It is concluded that the prevalence of smoking is high, that women are starting to smoke earlier than men and that no effort is being made to stop this habit.