Well-conducted telephone surveys provide an economical means of estimating the prevalence of sexual and reproductive behaviors in a population. There is, however, a nontrivial potential for bias since respondents must report sensitive information to a human interviewer. The National STD and Behavior Measurement Experiment (NSBME) evaluates a new survey technology—telephone audio computer-assisted self-interviewing (T-ACASI)—that eliminates this requirement. The NSBME embedded a randomized experiment in a survey of probability samples of 1,543 U.S. and 744 Baltimore adults ages 18 to 45. Compared with NSBME respondents interviewed by human interviewers, respondents interviewed by T-ACASI were 1.5 to 1.6 times more likely to report same-gender sexual attraction, experience, and genital contact. The impact of T-ACASI was more pronounced (odds ratio = 2.5) for residents of locales that have historically been less tolerant of same-gender sexual behaviors and for respondents in households with children (odds ratio = 3.0).