Three patients with lumbar anterior spinal fusion (two with Dwyer instrumentation) developed retroperitoneal fibrosis in relation to the operative site. This complication is possibly a reaction to the retroperitoneal insult. Haematoma, low-grade infection and metallic implant are other likely contributory factors. Its occurrence is affected by the laterality of surgical approach and extent of dissection. Radiologists should be aware of such a complication when investigating post-fusion patients. Early diagnosis and treatment prevent further renal damage.