Collecting accurate information on sexual behavior is vital for monitoring HIV and other STI risk and for evaluating interventions to reduce disease transmission. The use of audio computer-assisted self-interviewing (audio-CASI) provides more privacy than interviewer-administered questionnaires, and therefore may offer a means of improving measurement of sensitive or stigmatized behaviors. Numerous U.S. studies have found that significantly higher levels of sensitive and, in some cases, illegal behaviors (e.g., obtaining an abortion, engaging in same-gender sex, injection drug use or violent behavior) were reported using audio-CASI than in face-to-face interviews or paperand-pencil self-administered questionnaires. [1][2][3][4][5] Studies using audio-CASI have been conducted in a number of developing countries, including Kenya,6,7 Malawi, 8 Zimbabwe, 9 Thailand, 10,11 India, 12 Vietnam, 13 Brazil 14,15 and Mexico. 16 While computerized interviewing generally yielded higher reporting of risky behaviors than did standard face-to-face interviews in these studies, the findings were not always as compelling as those from studies conducted in the United States. In the developing world, effective use of computers for reporting sensitive behavior appears to depend in part on the types of questions asked, the setting and the study population.In addition to the many studies that have examined the effect of interview mode on reporting of sensitive behavior, a substantial body of research has assessed the consistency of self-reports in U.S. surveys, both within a single interview and, more commonly, across interviews in longitudinal surveys. These analyses revealed that discrepancies in reporting were not random. Rates of inconsistency varied by respondent characteristics, such as gender, race, education and cognitive ability, as well as by the sensitivity of, or stigma associated with, the activity being reported; 17-20 that is, more stigmatized behaviors were associated with higher rates of inconsistency. 19,[21][22][23] Few studies have been conducted on the consistency of selfreports in developing countries, 23,24 and we are aware of only one that has explored the effect of interview mode on consistency of reporting. 6 We conducted a randomized study of audio-CASI versus face-to-face interview reporting of reproductive behavior, sexual behavior, contraceptive use, prior STI infection, and alcohol and drug use among women in São Paulo, Brazil. In a previous analysis, we found that audio-CASI produced higher reporting of risky sexual behavior than did face-toface interviews at the enrollment visit. Moreover, stronger associations between risky behavior and STI infection were observed in data collected via the audio-CASI mode, with STI-positive women being more likely to underreport risky