[A 15-year-old boy with spontaneous pain in the lower leg].

On kicking the ball during a football tournament, and with no involvement of any other player, a 15-year-old boy experienced a spontaneous fracture of the tibia with no fragment displacement. The X-ray of the region of the fracture revealed a cystic structure measuring approximately 3 cm x 2 cm x 2 cm. After eight weeks of conservative treatment, radiography showed bony consolidation of the cyst, and the patient was pain-free. The differential diagnosis must give consideration to juvenile and aneurysmal bone cysts, giant cell tumors and malignant tumors (e.g. osteosarcoma and Ewing's sarcoma).