The international literature suggests that people are more likely to admit to using psychoactive substances by checking a box on a self-administered questionnaire—especially when the questionnaire is completed on a computer—than by answering an interviewer over the phone. Based on a comparison of two French surveys conducted in 2005—the Life Events and Health Survey (EVS) and the Health Barometer—this chapter analyzes the potential impact of the data collection method on the reporting of such practices by individuals aged 18 to 64. Unlike in the U.S., where there is unanimous agreement on the superiority of self-administered questionnaires, the results of the two surveys appear highly consistent here: the use of illicit drugs, reported using a self-administered computer-assisted interview with headphones (Audio-CASI) in the EVS survey, is found to be particularly close to that recorded in the Health Barometer conducted via telephone interview. Audio-CASI, however, seems particularly well-suited for reporting alcohol consumption. Analyses based on logistic models show that Audio-CASI appears to be better suited for young men, while the telephone offers more convincing results for women and older individuals. With some nuances, these two data collection methods appear, at first glance, to be well-suited for sensitive topics.[author’s abstract]