OBJECTIVE: To determine the appropriateness of an online forum compared with face-to-face interviews as a source of data for qualitative research on adherence to secondary prevention medications after stroke. DESIGN: A comparison of attributes of two data sources, interviews and a forum, using realistic evaluation; a comparison of themes around adherence according to the Perceptions and Practicalities Approach (PAPA) framework. SETTING: Interviews were conducted in UK GP practices in 2013 and 2014; online posts were written by UK stroke survivors and family members taking part in the online forum of the Stroke Association between 2004 and 2011. PARTICIPANTS: 42 interview participants: 28 stroke survivors (age range 61-92 years) and 14 caregivers (85% spouses). 84 online forum participants: 49 stroke survivors (age range 32-72 years) and 33 caregivers (60% sons/daughters). RESULTS: 10 attributes were identified within the two data sources and categorised under three domains (context, mechanisms and outcomes). Participants' characteristics of forum users were often missing. Most forum participants had experienced a stroke within the previous 12 months, while interviewees had done so 1-5 years previously.All interview themes could be matched with corresponding themes from the forum. The forum yielded three additional themes: influence of bad press on taking statins, criticisms of clinicians' prescribing practices and caregiver burden in assisting with medications and being advocates for survivors with healthcare professionals. CONCLUSIONS: An online forum is an appropriate source of data for qualitative research on patients' and caregivers' issues with adherence to secondary prevention stroke medications and may offer additional insights compared with interviews, which can be attributed to differences in the approach to data collection.