Penetrating wounds of the foot are not uncommon. Many are caused by thorns or by fragments of wood that are retained in the foot, creating a foreign-body granuloma. The differential diagnosis for bony reaction to an unrecognised organic foreign body includes osteoid osteoma, chronic and acute osteomyelitis, tuberculosis granuloma, bone cyst, aneurysmal bone cyst, cortical fibrous defect, and neoplasm. We report the case of a boy suffering from a thorn inducing a lytic lesion of the fifth metatarsal that demonstrates the diagnosis difficulties of foreign body granuloma.