Two patients, a woman aged 65 years and a man aged 56 years, with cancer, presented with pain in one leg as the first manifestation of metastases. The woman had tumour plexopathy of the lumbosacral plexus caused by an os sacrum metastasis of a thyroid carcinoma; she received radiotherapy but died a short time later. The man had lumbosacral epidural metastases of a colon carcinoma, compressing lumbosacral roots; with radiotherapy he survived the first year. Back pain with radiating pain is a frequent symptom in patients with cancer. Spinal epidural metastases, spinal and paraspinal metastases without epidural extension, tumour plexopathy and leptomeningeal metastases are the commonest causes. Early diagnosis (by MRI or spinal fluid examination) is important; with progressive weakness or sphincter disturbances the prognosis worsens.