Primary and secondary care services are charged with failing to adequately detect and treat mental disorder in older adults due to the ‘understandability phenomenon’; the belief that mental disorder in old age is inevitable and therefore not worthy of intervention. Quantitative data appear to support this hypothesis but lack the explanatory power of detailed accounts. Nine general practitioners (GPs) participated in group interviews about their assessment and treatment of older patients, and their expectations and experience of referral to secondary care. Resulting transcripts were subject to Thematic Analysis. Respondents recognised the unique features of these clients, and their impact on the detailed, recursive processes of assessment, clinical decision-making and intervention. GPs described confidence in managing most cases of mental disorder, describing the role of secondary care as one of consultancy in extreme or unusual cases. GPs did view mental disorder as commonly originating in adverse circumstances, and queried the validity of pharmacological or psychological interventions in these cases. They did not, however, equate understandability with acceptability, and called for social interventions to be integrated with health-care interventions to tackle the cause of mental disorder in older adults. At a wider level, findings highlight the discrepancy between assumptions about GP attitudes and actions, and their own accounts. At a local level, findings will assist in focusing secondary care service development where need is perceived, into consultancy and training.