Increasing attention has focused on the medical risk to young, unmarried, sexually active adults of contracting sexually transmitted diseases (STDs) in general and acquired immunodeficiency syndrome (AIDS) in particular. Yet little is known empirically about the extent to which this group perceives themselves to be at risk for contracting specific STDs or is changing their behaviors to reduce their risk. In the current study, the authors report findings from two matched samples of unmarried young adults, 182 assessed in the winter of 1986 and 182 in the fall of 1987. Results demonstrated greater worry and concerns about all STDs, including AIDS, in the second sample assessed than in the first. Some behavioral changes also were noted in the second group, including increased use of condoms. Nevertheless, 44% of sexually experienced participants in the fall of 1987 reported that they had not changed their behavior in any way to reduce their risk of acquiring human immunodeficiency virus (HIV) infection.