The Internet is rapidly becoming a third party in the doctor-patient relationship. The World Wide Web, electronic mail (e-mail), and discussion groups have dramatically increased the quantity of medical and health information available to patients, who, in turn, vary greatly in their understanding of that newly discovered information. This article reviews the advantages and disadvantages of the Internet for both oncology patients and physicians. This forms the background for a discussion of three steps that clinical oncologists and other health care professionals can take to direct and control the potential of the Internet so as to optimize patient care. These steps include: (1) finding out what type of cancer information is being disseminated on the Web; (2) using Internet-derived material that patients bring to the clinic as a stepping-stone for patient education; and (3) becoming an active participant on the Web. Each of these strategies requires health professionals to be proactive. The appropriate and effective use of the Internet, as well as its boundaries, are rapidly expanding in medicine and are likely to co-evolve with changes in patient-health care provider relationships.