The oomycete Pythium insidiosum is the pathogenic cause of pythiosis, a life-threatening disease that affects several animal species. Canines are the second most affected species, and the disease is characterized by the development of cutaneous and gastrointestinal lesions. While concomitant cutaneous and gastrointestinal lesions are rarely found in the same animal, this report documents a case of concurrent cutaneous and gastrointestinal pythiosis in an 18-month-old female Labrador. This dog had an ulcerative cutaneous lesion on the right thoracic region for 12 months that was unresponsive to itraconazole and terbinafine therapy. Two months prior to death and concurrent with the cutaneous lesion, the dog became anorexic with frequent vomiting and bloody stools. At necropsy, a cutaneous lesion that extended subcutaneously into the intercostal muscles was observed. Additionally, the large intestine contained two lesions that caused luminal narrowing. Organs were collected, routinely processed and stained using hematoxylin and eosin and Gomori methenamine silver. Histological examination of the lesions in the large intestine and on the skin revealed areas of necrosis surrounded by a pyogranulomatous infiltrate. Occasionally, black, septate, branching hyphae were detected following staining with Gomori methenamine silver. The diagnosis of pythiosis was confirmed using immunohistochemical methods. This report describes the occurrence of concomitant gastrointestinal and cutaneous lesions in a dog and highlights the therapeutic difficulties encountered with this disease.