In May 2000, AstraZeneca launched a Web service for asthma patients and health-care providers called LinkMedica, which includes an asthma diary for monitoring and self-management. In the diary, the patient enters his or her peak flow, number of doses of rescue medication, and if there have been any asthma symptoms during the previous 24 hours. The patient receives an immediate response from LinkMedica, telling him or her if the asthma is under control and what to do if not, eg, increase the dose of inhaled steroid. Health-care providers have access to the patient diary.The primary objective of the study was to describe patients' and health-care providers' use of LinkMedica. Secondary objectives were to evaluate their perception of the system and how the users' interaction with the system is influenced by their everyday lives.Site statistics regarding number of registered users and diary usage were analyzed. An online survey among users (85 respondents), a mailed questionnaire to health-care providers (131 respondents; response rate 26.8%), as well as in-depth interviews with 10 patients and 5 general practitioners, elicited further quantitative and qualitative data on users' perceptions.In February 2003, a total of 7653 users had registered. During 2002, the growth in registered users averaged 50 per month. In the same period, the number of unique diary users per month decreased from 307 to 138. Patients usually stopped using the diary after a short time; the doctors were reluctant to introduce the diary to patients because of time constraints. Several user subtypes were identified among patients and their relatives.The self-selected survey responses and in-depth interviews indicated that LinkMedica is generally considered a trustworthy and reliable site by both patients and doctors. However, there was a contrast between users' positive perception of LinkMedica and their unwillingness to use the site for more than short periods. The primary reason for this was that LinkMedica did not fit into their everyday lives because of technical and psychological aspects. A number of recommendations to improve LinkMedica are suggested.