Recent data indicate that nearly one in three Bolivian adolescent females becomes pregnant prior to reaching age twenty. This article presents the results of a study undertaken to address the question of why some female adolescents in La Paz, Bolivia, become pregnant while others in similar circumstances avoid early pregnancy. The study utilized mixed qualitative-quantitative methods based on a case-control design. Among the potential explanatory factors considered were family structure, parental relationships, partner relationships, knowledge of pregnancy risks, self-esteem, and locus of control. Significant differences between girls experiencing a pregnancy and those who had not were observed on two of the six factors considered-relationships with parents and self-esteem. Girls who had experienced a pregnancy were less likely to have reported affectionate and supportive parents, more likely to have reported fighting in their home, and exhibited lower levels of self-esteem than those who had never been pregnant. Focus-group discussions suggested that adolescent females in La Paz lack trustworthy support networks that would empower them to seek information regarding sex and contraception and to act upon such information.