The microanatomy of one male and one female specimen of a zoonotic Onchocera sp in a fibrous nodule excised from the wrist of an Ontario resident, two bovine Onchocerca from Saskatchewan and Manitoba, Canada, and O. cervicalis from the ligamentum nuchae of a horse in Georgia, U.S.A., were compared. In dimensions and cuticular morphology, the three Canadian specimens of Onchocera shared certain features and closely resembled both O. cervicalis and O. gutturosa. The number of cuticular striae in some species of Onchocerca, particularly in male worms, is briefly discussed and its taxonomic value questioned. The Canadian patient visited Radlett, Hertfordshire, England, and then her summer cottage in the Muskoka region, Ontario, prior to the appearance of her symptoms, so that it is uncertain where she acquired the infection. Zoonotic onchocerciasis has yet to be described from Ontario. All nine cases of bovine onchocerciasis (the two described here and seven others) have occurred in Manitoba and Saskatchewan.