The natural history of 120 popliteal cysts in children has been reviewed. Of seventy untreated cysts fifty-one disappeared spontaneously during a mean period of one year and eight months. Of fifty cysts submitted to operation, twenty-one recurred in a mean period of seven months. Three children with recurrences had more than one further operation. Most popliteal cysts in children disappear spontaneously, and operation without very good reason is unjustified.

Summary Seventy-three knees which had undergone patellectomy for patello-femoral osteoarthritis are reviewed. A possible mechanism of involvement of the tibiofemoral joint is described. Patellectomy, when the disease is confined to the patello-femoral articulation, appears to be beneficial over a 5-year period. When arthritic changes are present in the tibio-femoral joint, patellectomy may be beneficial in about half the patients.