This paper presents the factors associated with caesarean section in primiparous adolescents in Brazil using data from a national hospital-based survey conducted between 2011 and 2012. Information was obtained from postpartum women through face-to-face and telephone interviews and a theoretical model with three levels of hierarchy was used to analyze associations with the dependent variable mode of delivery (caesarean or vaginal). The results show that the caesarean section rate among primiparous teenagers is high (40%). The most significant contributing factors for caesarean section were: considering this mode of delivery safer (OR=7.0; 95%CI: 4.3-11.4); giving birth under the private health system (OR=4.3; 95%CI: 2.3-9.0); being attended by the same health care professional throughout prenatal care and delivery (OR=5.7; 95%CI: 3.3-9.0) and clinical history of risk and complications during pregnancy (OR=10.8; 95%CI: 8.5-13.7). Adolescent pregnancy continues to be an important concern on the reproductive health agenda and the rates observed by this study are worrying given the effects of early exposure to caesarean section.