While the Internet has the potential to educate persons living with HIV/AIDS (PLWHA), websites may contain inaccurate information and increase the risk of nonadherence with antiretroviral therapy (ART). The objectives of our study were to determine the extent to which PLWHA engage in Internet health information seeking behavior (IHISB) and to determine whether IHISB is associated with ART adherence. We conducted a survey of adult, English-speaking HIV-infected patients at four HIV outpatient clinic sites in the United States (Baltimore, Maryland; Detroit, Michigan; New York, and Portland, Oregon) between December 2004 and January 2006. We assessed IHISB by asking participants how much information they had received from the Internet since acquiring HIV. The main outcome was patient-reported ART adherence over the past three days. Data were available on IHISB for 433 patients, 334 of whom were on ART therapy. Patients had a mean age of 45 (standard error [SE] 0.45) years and were mostly male (66%), African American (58%), and had attained a high school degree (73%). Most (55%) reported no IHISB, 18% reported some, and 27% reported ''a fair amount'' or ''a great deal.'' Patients who reported higher versus lower levels of IHISB were significantly younger, had achieved a higher level of education, and had higher medication self-efficacy. In unadjusted analyses, higher IHISB was associated with ART adherence (odds ratio [OR], 2.96, 95% confidence interval [CI] 1.27-6.94). This association persisted after adjustment for age, gender, race, education, clinic site, and medication self-efficacy (adjusted odds ratio [AOR] 2.76, 95% CI 1.11-6.87). Our findings indicate that IHISB is positively associated with ART adherence even after controlling for potentially confounding variables. Future studies should investigate the ways in which Internet health information may promote medication adherence among PLWHA.