Of 3,923 special intervention participants in the Lung Health Study who were offered nicotine gum to help them quit smoking, 1,080 (28.9%) were using nicotine gum 12 months after entry into the study. This group is comprised of 33.6% sustained nonsmokers, 54.5% intermittent smokers, and 19.2% continuing smokers. The average use of gum at 12 months is 7.3 pieces per day. At 12 months, men were significantly more likely to be nonsmokers than women, but women were significantly more likely to use gum than men. Among the sustained nonsmokers, continuous gum users reported significantly more mild side effects than those who used gum intermittently, although there were no differences in moderate or severe side effects between the two groups. Overall, the rate of observed side effects was small. Factors associated with nicotine dependence were related to the use and amount of gum use at 12 months.