A simple bone cyst of the proximal humeral metaphysis was found to cause growth disturbance with shortening and deformity in four patients. All had one pathological fracture. Three of them were treated with cortisone injections; the fourth patient, who presented an erosion of the physis, was treated with saline solution irrigation. Four hypotheses about the aetiology of growth arrest in the evolution of this benign lesion, are discussed: iatrogenic lesion of the physis, growth plate involvement by fracture, cortisone injection, and increased cyst pressure leading to erosion and even perforation of the growth plate.