For some Dirofilaria spp. of zoonotic importance, such as D.immitis, D.tenuis, D.ursi, reviews of human cases were often published. For D. repens there is no published information giving a picture of the importance of the problem and of the geographical distribution of the parasite in the world. From a study of the international literature and from direct experience (our workgroup observed 75 cases in Italy) we have ascertained that the condition associated with D. repens is the most frequent and the most widely distributed in the world, of the dirofilariases of medical relevance: comprehensively 397 cases were recorded in 30 countries, exclusively in the Old World, with endemic foci in Southern and Eastern Europe, Asia Minor, Central Asia and Sri Lanka. Apparently, the most affected country is Italy with a total of 168 cases. The most common localisations are the subcutaneous (normally nodular) and the submucosal (nodular or not). The most affected areas are the head, the thoracic wall and the upper limbs. However, 15 cases with internal localisations are recorded (9 of them being pulmonary) which were always diagnosed erroneously as malignant neoplasiae. Clinical diagnosis for the other localisations was also generally wrong with the exception of the subconjunctival cases, where because of the transparency of the bulbar conjunctiva, it is possible to see the parasite directly. The correct diagnosis is usually histological, based on the identification of the nematode using the morphological characters of the species to differentiate it from the other dirofilariae or other erratic nematodes. It is possible that the zoonosis in man is more frequent than shown by the literature: many cases are not diagnosed, viz. not published, others recover spontaneously without medical intervention.