Access to health information on the Internet has revolutionized how medical patients learn about their illnesses. Valuable information can be found online; however, many health Web sites contain inaccurate or misleading information. The authors surveyed 324 adults with HIV concerning their Internet use for obtaining health information. Health information found online was then rated for quality by participants and by medical professionals. Participants were less critical of health information found online than medical professionals and made smaller distinctions between high-quality and low-quality information. Assigning credibility to low-quality information was predicted by lower incomes and educational attainment, poorer reading comprehension, lower literacy levels, and irrational health beliefs. Results suggest that patients do not always evaluate online information critically and may be vulnerable to misinformation.