Patients are increasingly seeking health information on the Internet, but to the best of our knowledge, this has not been previously studied in haematology. We aimed to characterise online health information use and associated variables among adult outpatients in our tertiary-care centre in Flanders, Belgium. During a 6-week period, we distributed 477 anonymous self-administered questionnaires and received 451 (response rate 94.5%), of which 444 (93.1% of total) contained information on Internet use for health information, the primary outcome. Two hundred and thirty-two respondents (52.3%) had ever sought any health information online, and 187 (33.1%) conducted searches pertaining to their haematological disease in the past year. The latter was independently associated with younger age and a higher level of education in multivariate analysis. Internet users ranked the Internet higher and other resources lower as health information resources. Among Internet users, 196 (89.5%) would be interested in a list of reliable websites about their disease. Patients reported positive and negative aspects of online health information-seeking; it increased anxiety in some while it stimulated coping in others. We conclude that haematological patients commonly use the Internet for health information and report both positive and negative aspects of using this medium.