If there is one certainty in general practice, it is the inherent presence of uncertainty. Undifferentiated presentations are common in primary care and a firm diagnosis is elusive in many encounters. Very commonly, symptoms are vague, examination findings unclear, investigation results conflicting, and response to treatment inconsistent. Guidelines may be irrelevant or non-existent. As a result, uncertainty is intrinsic to the general practice encounter. Indeed, it has even been proposed that managing uncertainty is the ‘specialty’ of general practice. Supervisors play an important role in helping their registrars manage uncertainty in general practice – in essence ‘what to do when you don’t know what to do’.