Forty cases of congenital pseudarthrosis of the tibia were reviewed. The results were assessed so as to emphasise function rather than simply the presence or absence of union. At the time of review, 14 patients had undergone amputation; eight others had non-union or tenuous union. No surgical procedure except the Farmer operation (a composite skin and bone pedicle graft from the other leg) showed any clear superiority. Among the factors associated with a poor result were considerable shortening, older children, and rapid resorption of the bone graft. It is felt that congenital pseudarthrosis of the tibia is a biological problem and not merely a mechanical one; consequently biological approaches to its treatment are needed.