From 1998 to 2012, 42 dogs with spirocercosis referred to pathology Department of Veterinary Faculty, Tehran University. Frequency of spirocercosis was higher in October, November, December, January, February, March months. Averagely, the cases were 4.73 years old of age, so that 59.3 % of them were male. The major pathological findings were located in distal part of esophagus (57 %, n = 24), stomach (24 %, n = 10), and aorta (9.5 %, n = 4), respectively. In addition, 7 % (n = 3) were in esophagus and stomach, 2 % (n = 1) in esophagus and aorta, 42 % (n = 18) indicated pulmonary lesions with hyperemia, atelectasis, edema and pneumonia. In 35 % (n = 15) of cases were with hepatic lesions hyperemia and fatty change. However, 26 % (n = 11) cases demonstrated renal lesions with hyperemia, interstitial nephritis, and 24 % (n = 10) encompassed urinary bladder lesions with hyperemia and adhesive cystitis. Furthermore, sudden death occurred in 7 % (n = 3) as well as cachexia in 7 % (n = 3) cases. Some spirocercosis cases (12 %, n = 5) were accompanied by distemper disease, mixed mammary gland tumor (2 %, n = 1) and parasitic dermatitis due to demodicosis (9.5 %, n = 4). Presumably some of pathological findings were related or emerged by other sort of diseases such as distemper. © 2012 Indian Society for Parasitology.