Abstract Purpose: To assess the value of MR imaging (MRI) with regard to union, graft viability and proximal pole bone marrow status, after use of vascularized bone grafts for treating scaphoid nonunions. Materials and methods: Vascularized bone grafts from the distal radius were used to treat 47 scaphoid nonunions resulting from fractures or enchondromas. Clinical and imaging evaluation was used for the pre- and postoperative assessment of all patients. Apart of conventional radiographs obtained in all cases, 15 patients were also assessed postoperatively with MRI at 3 months. From these 15 patients, eight were assessed preoperatively with MRI whereas nine had serial MRI evaluations at 6 and 12 months. The clinical follow-up time of this subgroup of 15 patients ranged from 6 to 27 months. Results: All patients showed clinical signs of union within 12 weeks form the procedure and at the latest follow-up they experienced complete (10 cases) or almost complete (five cases) relief from pain. Both plain and contrast-enhanced MRI obtained at 3 months showed viability of the bone graft in all cases. At 3 months union was established with plain radiographs in 12 patients at both sides of the graft and in three patients between the graft and proximal pole. At 3 months plain MRI showed nonunion in four patients (two between graft and proximal pole, two between graft and distal pole and one at both sides of the graft) whereas contrast-enhanced MRI revealed only one case of nonunion between graft and proximal pole. Four patients were considered to have osteonecrosis of the proximal pole intraoperatively. Two of them showed necrosis of the proximal pole with preoperative and postoperative plain radiographs and three of them with plain postoperative MRI. Contrast-enhanced MRI at 3 months showed postoperative reversal of necrotic changes in all four scaphoids. MRI also revealed bone marrow oedema of the carpal bones surrounding the scaphoid in 14 cases. Serial MRI at 6 and 12 months, obtained in nine patients, revealed resolution of the bone marrow oedema of the surrounding bones and full graft incorporation in all cases. Conclusion: Contrast-enhanced MRI is able to demonstrate the early union after treatment of scaphoid nonunions with vascularised bone grafts allowing thus earlier mobilisation. In addition, MRI can assess the viability of the proximal pole and the graft as well as the postoperative bone marrow oedema-like lesions of the surrounding bones.