A study was made among students and instructors of three schools of nursing at São Paulo City, Brazil, on number of smokers, non smokers and previous smokers and the causes that led them to start smoking as well as to withdraw from the habit. In a population of 636 studients the authors found 24.1% smokers, 68.5% non smokers, 7.4% previous smokers. The percentage of 117 instructors were 23.1%, 62.4% and 14.5% respectively. The reason for start smoking most frequently mentioned by both groups was curiosity (35.2% and 28.2% respectively). For leaving the habit was conscience of damage to health (72.5% and 65.2%). For the non smokers this was the main reason for never starting the habit. The authors studied also the age of start smoking, number of cigarettes smoked per day. The outside influences for smoking or not orientation of others about the damages of smoking to health were also considered.