This case report describes an infiltrative lipoma in a horse. A slow-growing mass, detected early after birth, was present at the caudal aspect of the foreleg (antebrachium) of a 2-year-old gelding. Cytological features were that of a benign lipoma. Surgical resection was attempted but failed due to the infiltrative nature of the mass. Consequently, the horse was euthanized. Histopathology revealed an infiltrative lipoma. This tumor is histologically benign but surgical resection is usually impossible due to its infiltrative nature.