There is a lack of information regarding the attitudes of Québec's adolescents about breastfeeding and how others influence their opinions. The present study aims to describe attitudes and subjective norms of adolescent males and females toward breastfeeding and to determine whether these are related to gender, age, secondary education level, mother tongue, country of origin, feeding method as an infant, feeding method of siblings, and exposure to breastfeeding. Adolescents (N = 439) answered a questionnaire based on the theory of reasoned action. Both genders showed an overall positive attitude but negative subjective norms toward breastfeeding. Gender differences and relationships with external variables in terms of attitudes as well as subjective norms are presented. Possible avenues to promote breastfeeding are discussed.