Non-union of the radius and/or ulna is comparatively common in the treatment of forearm fractures. Bone graft from the iliac crest secured by rigid plate fixation under compression is indicated in non-unions with a bone defect longer than 2 cm. The aim of the study is to compare the results with the current literature. Thirteen patients (female: 1; males: 12), mean age 44 years (23–75 years), were treated in our department between 1993 and 2003. In 10 patients the original injury involved both radius and ulna; in the remaining three only the ulna was affected. All the fractures had been internally fixed, except for a radius fracture. Non-unions involved the ulna in eight cases, the radius in one case and both radius and ulna in four cases. A cortico-cancellous graft was used to fill a defect of the ulna in 11 cases and of the radius in two cases. In the non-unions of both bones only one bone was operated (one radius and three ulna); a different treatment was performed in the other bone. The mean time between the original injury and the indexed procedure was 7 months (3–14 months). The mean bone defect was 4 cm (2–6 cm). A T-shaped cortico-cancellous graft was always used. All the patients were evaluated clinically and radiographically with a mean follow-up of 4 years (1–10 years). Bony union was achieved in all the patients at an average time of 4 months (3–6 months). At the follow-up the mean elbow flexion was 130°, the mean extension lag 4°, the mean pronation 71° and the mean supination 61°. The mean grip strength was 38 kg, 81% of the contralateral side. Cortico-cancellous bone graft from the iliac crest is an effective technique to fill a bone defect of between 2 and 6 cm. Up to this length the mechanical properties of the graft are optimal for a rigid plate fixation under compression; moreover, biological conditions allow ready integration of the graft. Rigid fixation with cortico-cancellous bone graft from the iliac crest is a useful technique for forearm non-unions with a bone defect of between 2 and 6 cm.