The simple bone cyst is a common, benign, fluid-containing lesion, usually occurring in the metaphysis of long bones. The cause of the lesion is unknown. Growth arrest from a simple bone cyst occurs in approximately 10% of patients. The cause of growth arrest is uncertain and may be the result of fracture associated with the cyst, iatrogenic (eg, surgical curettage of a simple bone cyst abutting the physis and damaging the physis in the process), or direct extension of the cyst through the physeal plate into the epiphysis. The latter process can be well demonstrated by MRI.