A non-gravid female Onchocerca was found in histopathological sections of a biopsy specimen taken from a painful nodule in the wrist of a 57-year old woman in Oita, in southern Japan. Six species of Onchocerca have been found in animals in Japan: two in wild bovids, one in equids, and three in domestic bovids of which one, Onchocerca sp., is only known by the microfilaria and infective stage. Distinctive morphological features of the worm, including a three-layered thick cuticle with prominent annular ridges at wide intervals, high somatic muscles and narrow lateral chords, resembled those of O. gutturosa, one of the three bovine Onchocerca species transmitted in the Oita region. However Onchocerca sp., which is also transmitted in this region, cannot be excluded. An ELISA test of the patient serum suggests that infections by Onchocerca spp. might be distinguished from those by Dirofilaria immitis, of which the number of human cases is increasing in Japan.