Clinical trials usually use the relative risk (rate ratio or hazard ratio) to compare the effects of one treatment modality with others. However, the numbers needed to treat/harm (NNT/NNH) are sometimes used as another way of presenting an estimate of the effect of a medical intervention, pointing at the number of patients needed to be exposed over a certain period of time in order to achieve one beneficial or adverse event. For clinicians and patients, this is a very simple and clear tool to demonstrate the consequences of a specific intervention. Epidemiologists and statisticians are more cautious with interpretations of data of that sort. This article brings the relevant perspectives of a clinician, an epidemiologist and a statistician in regard to the value of NNT/NNH.