Tsogolo la Thanzi (TLT) was designed to study how young adults navigate sexual relationships and childbearing during a generalized HIV epidemic. TLT began in 2009 with a population-representative sample of 1,505 women and 574 men between the ages of 15 and 25 living in Balaka, southern Malawi, where regional adult HIV prevalence then stood at 15 percent. The first phase (2009-11) included a series of eight interviews, spaced four months apart. During this time, women's romantic and sexual partners enrolled in the study on an ongoing basis. A refresher sample of 315 women was added in 2012. Seventy-eight percent of respondents were re-interviewed in the second phase of TLT (2015), which consisted of follow-up interviews approximately 3.5 years after the previous interview (ages 21-31). At each wave, detailed information about fertility intentions and behaviors, relationships, sexual behavior, health, and a range of sociodemographic and economic traits was gathered by means of face-to-face surveys. Biomarkers for HIV and pregnancy were also collected. Distinguishing features include: a population-representative sample, closely spaced data collection, dyadic data on couples over time, and an experimental approach to HIV testing and counseling. Data are available through restricted data-user agreements managed by Data Sharing for Demographic Research (DSDR) at the University of Michigan.