The aims were to explore adolescent smokers' understanding and their physiological and psychological experience of addiction to nicotine and to assess the content validity of the Hooked on Nicotine Checklist (HONC), a 10-item measure of nicotine dependence in youth. Six focus group interviews were conducted with male and female smokers recruited by school staff from among known smokers at one English and two French high schools in Montreal. Participants were 64 high-school students aged 14-17 years. Measurements were focus group discussion of smoking patterns and levels for self and others; feelings and sensations while smoking; physical and mental experiences of urges, feelings and sensations when smoking is prohibited; the physical, psychological, and social meanings of being hooked, dependent, or addicted; levels of dependence, desire to quit, and quit attempts. Participants readily identified nicotine dependence as relevant to their smoking experience. Dependence was described as the need to smoke, sometimes experienced as sensations of emptiness in the chest or blood and sometimes as a feeling in the mind. Smoking urges were often situationally determined and associated with hunger. With the exception of feeling sad, blue, or depressed on smoking withdrawal, participants endorsed almost all the symptoms in the HONC as relevant to their experience of dependence and identified several other symptoms as well. Adolescents are able to provide self-reports of symptoms of dependence that are consistent with a theoretically driven conceptualization of nicotine dependence. The HONC demonstrates content validity among adolescents but could be improved through removal of the item related to depression on withdrawal and possibly addition of items related to stress and appetite.