Plasma cotinine levels were measured in 137 students (ages 14 to 17 years), as an independent validation of self-reported cigarette smoking status. Ninety-five per cent of the students who reported daily cigarette smoking had detectable cotinine levels. In contract, only 2 per cent of students who reported that they never smoke cigarettes had detectable levels of plasma cotinine. Results suggest that adolescents can report accurately on their smoking status if sufficient assurance of confidentiality is stressed.