BACKGROUND: Online self-management diaries are used to support patients' self-management skills and facilitate associated behavioral changes. Although web-based diaries are well-known as a potential self-management tool, reasons that patients use (or do not use) self-management diaries, as well as perceptions and behaviors related to diary use, remain largely unknown. METHODS: Semistructured interviews (n ؍ 30) were conducted with health-care professionals and subjects to understand perceptions and behaviors related to self-management diary use for asthma and COPD in 2 hospitals in Rotterdam, The Netherlands. RESULTS: Subjects in this study used self-management diaries to improve their knowledge of the disease, cope more consciously with their disease, feel in control, and discuss outcomes from the self-management diaries with their health-care professionals. Two subjects reported that they used the self-management diary to cope more effectively with their disease and recognized an exacerbation and acted by adjusting their medications. Both health-care professionals and subjects experienced practical barriers in integrating self-management diaries into their regular practices. Subjects' reasons for nonuse were related to the intervention, the disease, and subject-provider contact. CONCLUSIONS: Health-care professionals should help patients use self-management diaries by collaboratively developing an individual treatment plan and by showing patients how to use the diaries to recognize and act on an exacerbation. Together with the suggestions made for improving the self-management diaries, this will aid in the integration of self-management diaries into regular health-care practice and enhance patients' self-management of their disease.