We reviewed 32 children after the treatment of simple bone cysts by intralesional injections of methyl-prednisolone acetate. The age of the child and the activity and size of the cyst did not significantly affect the radiological outcome. The earliest time at which the radiological response could be reliably determined was three months. After a median period of review of five years, four (13%) cysts had healed, 20 (62%) cysts were partially visible but sclerotic, four (12.5%) were still visible but opaque and four (12.5%) were clearly visible. The healed and partially visible but sclerotic cysts were classified as having satisfactory radiological healing. This was observed in 13 of 32 cysts (41%) after the first injection, in eight of 21 (38%) after the second injection, but in relatively few of the remaining cysts after subsequent injections. A satisfactory symptomatic outcome was achieved in all of the 18 children with humeral cysts and in the one child with a fibular cyst irrespective of the radiological outcome, but only in nine (67%) of the 13 children with femoral or tibial lesions, in whom the cysts were healed or sclerotic. The remaining four children had exertional bone pain and repeated fractures of their femoral or tibial cysts which were incompletely healed with sclerosis in one and opacities in three. We conclude that the healing response to intralesional corticosteroids is unpredictable and usually incomplete even after
