Filaria martis causes a poorly known subcutaneous filariosis in mustelids. Few information is available about lesions that F. martis causes in beech martens, on its morphology, biology and the occurrence of the infection. From 1997 to 2006, 29 beech martens from two sites of southern Italy (Sites A and B) have been necropsied. Ectoparasites and nematodes were collected and morphologically identified. A variable region of the cytochrome c oxidase subunit 1 (cox1) of F. martis has been characterised to compare females presenting caudal tips smooth without spines (i.e. Morphotype 1-Mrph. 1) and with spines (i.e. Mrph. 2). All ticks collected were identified as Haemaphysalis erinacei. Eleven animals from Site A were found infected by F. martis nematodes in subcutaneous tissue in both membranous capsules or free under the inner skin surface. The most important morphological characters of F. martis have been reported and discussed. The molecular analysis showed 100% homology among cox1 sequences from Mrph. 1 and 2 thus indicating that the shape of female posterior edge may vary among specimens of F. martis. The results here presented provide new insights into the biology, ecology and morphological characteristics of this scantly known nematode.