Numerous factors which promote human trafficking have been examined by many scholars, yet little attention has been placed on the role of adolescent single mothers as a significant factor that increases the vulnerability of these young women to trafficking. This study aims to understand and explain why two countries with similar characteristics in geography, political and socio-economic systems present a very different picture in their sex trafficking patterns and challenges. This is a case study that compares Argentina and Brazil along a variety of indicators relevant to human trafficking. Although similar with respect to several characteristics analyzed in their incidence of sex trafficking, Argentina and Brazil do differ in one major factor that on its face could account for the differences in their sex trafficking practices --birth rate among adolescent girls aged 15 to 19. This rate is higher in Brazil than that in Argentina. This study seeks to answer the following questions: 1. - Does this difference account for the difference in sex trafficking practices and if so, how? 2. - Is this difference explained by something else (e.g. other than birth rate)? 3. - What other factors might contribute to the difference in sex trafficking practices? Two main sources of information were used in this comparative analysis: (1) data collected from reports, databases from intergovernmental organizations, governmental agencies, NGOs, and academic literature; and (2) court sentences from both countries, to both flesh out the factors identified, and more importantly, to support or refute the assumption with respect to the role of adolescent birth rates. Both qualitative and quantitative analyses were employed. This study reveals four main differences between Argentina and Brazil that collectively, indeed, shed light on their sex trafficking differences: 1) methods of recruitment, 2) “modus operandi” and government complicity, 3) gender inequality and 4) the incidence of teen single motherhood as a vulnerability factor to trafficking. Findings in this study suggest that matrifocality, the woman-centered family, is a key component in understanding how and why Brazilian adolescent single mothers are an easy target for traffickers.