ObjectiveTo explore whether a preconsultation web-based intervention enables patients with diabetes to articulate their agenda in a consultation in the hospital outpatient clinic with their diabetologist.Methods and designA qualitative study embedded in a pragmatic pilot randomised controlled trial.SettingTwo city outpatient departments in England.Participants25 patients attending a follow-up consultation and 6 diabetologists.InterventionThe PACE-D, a web-based tool adapted for patients with diabetes to use before their consultation to generate an agenda of topics to discuss with their diabetologist.Data collection25 participants had their consultation with their diabetologist audio-recorded: 12 in the control arm and 13 in the intervention arm; 12 of the latter also had their PACE-D intervention session and a consultation recorded. Semi-structured interviews with 6 diabetologists, and 12 patients (6 in the intervention group and 6 in the control group).AnalysisThematic discourse analysis undertaken with patient representatives trained in qualitative data analysis techniques.ResultsWe identified four consultation types: diabetologist facilitated; patient identified; consultant facilitated and patient initiated and patient ignored. We also identified three critical aspects that explained the production and utilisation of the agenda form: existing consultative style; orientation to the use of the intervention and impact on the consultation. Where patients and diabetologists have a shared preference for a consultant-led or patient-led consultation, the intervention augments effective communication and shared decision making. However, where preferences diverge (eg, there is a mismatch in patients' and diabetologists' preferences and orientations), the intervention does not improve the potential for shared decision making.ConclusionA simple web-based intervention facilitates the articulation of patients’ unvoiced agenda for a consultation with their diabetologist, but only when pre-existing consultation styles and orientations already favour shared decision making. More needs to be done to translate patient empowerment in the consultation setting into genuine self-efficacy.Trial registration numberISRCTN75070242.