Exchange nailing for failure of union after primary intramedullary nailing of the tibia is widely used but the indications and effectiveness have not been reported in detail. We have reviewed 33 cases of uninfected nonunion of the tibia treated by exchange nailing. This technique was successful without open bone grafting in all closed fractures and in open fractures of Gustilo types I, II and IIIa. The requirement for open bone grafting was reduced in type-IIIb fractures, but exchange nailing failed in type-IIIb fractures with significant bone loss. For these we recommend early open bone grafting. The most common complication was wound infection, seen more often than after primary nailing. We discuss our protocol for the use and timing of exchange nailing of all grades and types of tibial fracture.