Peripheral neuropathy is a common condition with a variety of causes. In some cases the neuropathy is the first symptom of an underlying malignancy. The frequency of occult cancer in patients with neuropathy is of importance in planning the investigations and follow-up of these patients. This retrospective study examined the incidence of cancer-related neuropathy among patients originally diagnosed with idiopathic peripheral neuropathy. Between 1981-1995 our department discharged 187 patients with the diagnosis of idiopathic peripheral neuropathy. Their names were cross-matched with the Norwegian Cancer Registry, and the medical records of the patients with known cancer were reviewed. In 14 patients (7.5%) we found cancer as the probable cause of the peripheral neuropathy originally classified as idiopathic. In eight of the patients the neuropathic symptoms preceded the tumour. In six cancer was already diagnosed when the neuropathic symptoms developed, but in three of these the neuropathy heralded a tumour recurrence. Idiopathic progressive neuropathy should always raise the suspicion of an underlying malignancy, especially if there are atypical accompanying symptoms and signs.