The authors analyse the etiology and treatment of 18 pseudarthroses of the tibial diaphysis occurring in a series of 320 fractures of this bone. This complication seldom appears in simple fractures treated by a plaster cast (two cases out of 144). In addition to classical and well known factors, it appears that pseudarthrosis occurs more frequently after traction-immobilization (10 cases out of 73), when the fragments had to be repositioned on many occasions under plaster cast, or in cases of open fractures. The treatment by bone grafting, principally in-lays, with or without plates and visses, yield satisfactory results.