The task of confirming a diagnosis of multiple sclerosis (MS), one of the commonest neurological disorders affecting young adults, has altered significantly in the magnetic resonance imaging era. Conversely, key principles, most notably objective documentation of neurological dissemination in time and space, remain fundamental to the process. Clinical acumen and experience are equally as crucial as an ability to interpret relevant investigations. Recognising typical clinical patterns, addressing potential 'mimics', and stratifying prognosis of a clinically isolated syndrome are just some of the challenges inherent in diagnosing MS.