The objective of this study was to examine the impact of belief about transmissibility of AIDS and concern about the disease on perceived changes in premarital sexual practices. It was posited that changes in sexual practices are most likely to occur when college students have more certainty about AIDS transmission and greater concern about AIDS. Based on this proposition, dating patterns, premarital sexual permissiveness, attitudes toward homosexuality, sexual orientation, and students' objective perception of AIDS as a problem were used as predictors of concern about AIDS and certainty of sexual transmission. Using a sample of 587 students in the state universities of California and Iowa and focusing on one type of sexual practices (i.e., condom use), it was found that concern about AIDS strongly increases the likelihood of using condoms. Contrary to our prediction, certainty about sexual transmission of AIDS was found to have a marginal effect on students' likelihood of condom use. Furthermore, it was found that monogamous dating, sexual permissiveness, and the degree of perception of AIDS as a problem significantly increase the likelihood of condom use if they are mediated by personal concern about AIDS. The implications are discussed with respect to the usefulness of a theoretical approach and its findings for education on AIDS prevention among college students.