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A case of myositis ossificans circumscripta in an eight-year-old, male, Weimaraner dog, is described. The animal was originally submitted with presumptive diagnosis of hernia. The lesion was a firm, subcutaneous nodule, 5 cm long by 3 cm width, localized in the right perineum muscles. After the radiologic study the lesion was interpreted as a neoplasm from coccygeal vertebrae. The surgical procedure to eliminate the neoplastic tissue confirmed its hardness. Excision was not complete and the sample was submitted to pathology. The mass was hard, well circumscribed, vascularized and surrounded by muscle tissue. The histopathological study revealed a heterotopic ossification with zones of atrophy, degeneration and muscle necrosis, alternating with zones of trabecular ossification toward the periphery, limited by abundant fibrous connective tissue. These findings are characteristic of myositis ossificans circumscripta. This case represents the first report in a dog in Mexico, of a condition resembling the myositis ossificans circumscripta in humans. [ABSTRACT FROM AUTHOR]