Several limitations to our study warrant further discussion. First, this study was crosssectional; thus, causal inferences cannot be made. Second, Add Health questions related to anal sexual intercourse were asked only in a section on detailed relationships. However, 1852 young adults in our sample did not complete this section (2.8% of these tested positive for trichomoniasis). Consequently, we were unable to adjust for anal sexual intercourse as a risk factor, and we used sexual orientation as a crude proxy.