This study is an article extracted from "Studies in family Planning", special issue on Adolescent Sexual and Reproductive Health in Sub-Saharan Africa, published in December 2008. The inconsistency between reported sexual behavior and HIV incidence has prompted some epidemiologists to question the conventional explanation for the African AIDS pandemic. This study represents one effort to investigate the reporting of premarital sex in rural southern Malawi. It summarizes the results from an interview-mode experiment conducted with unmarried young women aged 15-21. Data concerning sexual behavior obtained from audio computer-assisted self-interviewing (ACASI), a technique designed to collect data on sensitive issues, are compared with data obtained from conventional face-to-face interviews. The study builds on earlier research conducted in two districts in Kenya where the authors first investigated whether the use of ACASI is feasible in developing countries and whether it provides more accurate information than interviewer-administered and self-administered questionnaires. In both Malawi and Kenya, the mode of interviewing and questions about types of sexual partners affect the reporting of sexual activity. Yet the results are not always in accordance with expectations. Reporting for "ever had sex" and " sex with a boyfriend" is higher in the FTF mode. When we ask about other partners as well as multiple lifetime partners, however, the reporting is consistently higher with ACASI, in many cases significantly so. The FTF mode produced more consistent reporting of sexual activity between the main interview and a subsequent interview. The association between infection status and reporting of sexual behavior is stronger in the FTF mode although in both modes a number of young women who denied ever having sex test positive for STIs/HIV.