The present study extends the theoretical framework of cognitive-developmental theory in order to examine the development of children's ideas about smoking, its causes, and consequences. Using Piaget's clinical method, the authors examined the concepts of smoking of three different age groups: 4-, 7-, and 11-year-olds (Ntotal= 72). The results revealed three major types of explanation consistent with the major stages of cognitive development as articulated by Piaget. Within two of these major categories, two subtypes were further distinguished. Thus, five developmentally ordered explanations of the consequences and causes of smoking were derived. Implications for clinicians, health practitioners, and health educators are described.