We consider whether there are situations in which 'shared decision making' in primary care is inherently problematic, such as in the demand for antibiotics to treat viral disorders. In such an instance there might be a lack of the equipoise necessary for a decision-making context in which apparent choices are genuine options. Using the techniques of discourse analysis on the transcript of a consultation with the parents of an infant with tonsillitis, we illustrate how a general practitioner's (GP's) efforts to reach a 'shared decision' come unstuck through a combination of the embedded power imbalance and the conflict between the GP's own prescription preferences and those of the parent.