Tinnitus is a common experience with up to one third of the adult population experiencing it at some time in their life. Less than 1% of the adult population have tinnitus of sufficient severity to affect their quality of life seriously (although up to 8% may seek medical advice about it). Much of the severity of tinnitus relates to the individuals' psychological response to the abnormal tinnitus signal. The prevalence of tinnitus increases in association with high frequency hearing loss. There is, unfortunately, no diagnostic test that either confirms the presence of tinnitus or its severity. Currently there is no satisfactory severity grading system. A five-point severity grading scheme is therefore proposed and the entry criteria detailed. The five severity points are: slight, mild, moderate, severe and catastrophic. Categorization as 'severe' or 'catastrophic' should be, by epidemiological definition, very rare. General guidance, theory and evidential support are contained within.