Three patients with mental neuropathy ("numb chin syndrome") secondary to systemic cancer are described. Two patients had malignant lymphoma and one a probable hypernephroma. In 2 patients, facial numbness was a presenting symptom of the malignancy. Investigations disclosed metastatic lesions of the mandible in one patient and cerebrospinal fluid was normal in 2 patients. Two patients died at 1 and 8 months respectively after onset of the neuropathy. Although benign in appearance, numb chin syndrome is most often, and sometimes initially, associated with visceral neoplasia or malignant hemopathy. It is a factor of poor prognosis. The pathogenesis is related either to metastasis of mandible, or neoplastic infiltration of the nerve itself.