To estimate the percentage of men who have sex with men (MSM) who have used the Internet to look for sex partners and to examine the prevalence of risky sex among MSM who have and have not sought partners online. Meta-analyses were conducted on findings from published English-language studies. High-risk sex was self-reported unprotected anal intercourse (UAI). Analyses were stratified by method of study recruitment (online versus offline venues) and participants' human immunodeficiency virus (HIV) status. In studies that recruited MSM offline, a weighted mean, based on 15 findings, indicated that 40% (95% confidence interval [CI], 35.2%-45.2%) of MSM had used the Internet to look for sex partners. In 3 findings from offline studies that stratified by participant HIV status, the weighted-mean percentage was higher among HIV-positive (49.6%; 95% CI, 44.9%-54.3%) than HIV-negative/unknown MSM (41.2%; 95% CI, 36.8%-45.6%). UAI with male sex partners was more likely among MSM who sought partners online than MSM who did not (odds ratio, 1.68; 95% CI, 1.18-2.40; k = 11). This group difference was observed for UAI with HIV-serodiscordant as well as HIV-seroconcordant partners, particularly among HIV-positive study participants. HIV-serodiscordant UAI was not more prevalent with partners met online than offline. A substantial percentage of MSM use the Internet to look for sex partners, and those who do are more likely to engage in unprotected sex. Additional research is needed to determine whether the Internet may increase risk behavior beyond that which occurs when men meet partners at offline venues.
