The World Wide Web (www) recently became an important source of health information for both physicians and patients. This work focuses on the information about allergic rhinitis and rhinosinusitis available in Portuguese in the Web. We assessed sites randomly selected from those listed by search engines (AltaVista, Yahoo!, Radix, Cadê?, America OnLine), consisting of samples of 50 sites on allergic rhinitis, 18 on rhinosinusitis and 107 on sinusitis. Twenty-two (40%) sites about allergic rhinitis contained scientific information, 3 (13,6%) of which presented misinformation. From 107 sites about sinusitis, 57 (53,3%) were directed to patients, and only 15% contained information for physicians. Many medicines and unconventional therapies for rhinosinusitis were available in the Web, however without warning for medical care. The authors conclude that quantity and quality of information about allergic rhinitis and rhinosinusitis published in Portuguese in the Web are not enough to satisfy physicians nor patients.