The present paper reflects the author’s personal observations concerning the notion of  focal infection and its necessary delimitation from other disease conditions. First of all, the author debates the general framework of the very concept of focal infection, which is often associated with various interpretations. Further, the author  presents a set of criteria serving for the concrete delimitation between the focal infection and the focus of infection localised in a certain area. The most important criteria seem to be the profile of the local inflamation, the level achieved by tissue  hypersensitivity and that of the local microbian presence, as well as the resulting clinical consequences.