The aim of this study was to explore the percentage of Dutch patients using the Internet to search for information about their illness. In addition, we studied patients' usage of health-related Internet applications, such as online patient support groups. The final objective of this study was to explore which demographic, health and psychological characteristics are related to patients' health-related Internet use. In order to answer these research questions we sent a written questionnaire to a representative sample of patients with breast cancer, rheumatoid arthritis and fibromyalgia. The overall total response rate was 69% (N = 679). In total, 52% of the patients used the Internet to search for information about their illness. However, only 15% of the respondents had ever read along with an online patient support group. An even smaller proportion of the patients (4%) had send postings to such a group. Online communication with health professionals was not commonly practiced. A younger age, a higher education and employment appeared to be the only significant predictors of patients' health-related Internet use. Patients' health-related Internet use could not be predicted by health and psychological characteristics. Although, about half of the patients made use of the Internet for health-related reasons, mostly their health-related Internet use was restricted to seeking information about their illness.