Abstract Background Although there is broad consensus that health-care priorities need to be set, there is little agreement about either the best principles or best methods for decision making. The only clear consensus to emerge between clinicians, academics, and policy makers is that decisions should be undertaken as systematically and accountably as possible, a demand that has been only partly met by the establishment of national bodies such as the UK National Institute for Health and Clinical Excellence (NICE). However, the individual nature of clinical decision making, local funding constraints, and the patchy availability of NICE guidance mean that a large element of priority setting goes on in consultations. We used a case study of morbid obesity surgery to investigate prioritisation processes and investigate how acceptable current decision making is to clinicians and patients. Methods 11 clinicians and 22 patients were recruited from a specialist centre for morbid obesity surgery and a series of consultations were recorded in a period of roughly 1 year. Clinicians and patients were interviewed before their first consultation and patients were interviewed again after each appointment. Patients were recruited purposively to ensure diversity in terms of age, sex, body-mass index, and main clinician consulted. Analysis was undertaken with a constant comparative approach, which entailed identification of common themes in the data through reading and re-reading of transcripts and use of matrices to compare the occurrence of themes across participants and over time. Contradictory cases were examined with interest and used to elucidate themes in the whole dataset. Findings Although all patients were eligible for surgery according to NICE guidance, clinicians used several additional criteria to prioritise patients for treatment in an attempt to make the best use of available resources. Although patients were told about these additional criteria for accessing treatment, which included a 10% weight loss and evidence of sustained behaviour change, clinicians rarely mentioned financial constraints on treatment availability, and were never prompted to do so by patients. However, follow-up interviews showed that all patients were aware of financial constraints on decision making, and most interpreted the additional access criteria in the context of health-care rationing. Nearly all patients said they would prefer clinicians to be more upfront about the effect of financial constraints on care, but were reluctant to challenge them directly for fear of disrupting the doctor–patient relationship or jeopordising their chances of accessing care. Interpretation The research findings suggest that a conspiracy of silence exists in consultations, whereby financial constraints on treatment are rarely discussed, increasing stress for many patients who are left uncertain as to the basis of decision making and the extent of advocacy offered by their clinician. In the context of continuing fiscal constraint and increased involvement of clinicians in financial decision making, we need to get a more complete understanding of priority-setting processes in consultations and to find out how these can be made as acceptable as possible to both clinicians and patients. Funding National Institute of Health Research.