Numb chin syndrome or malign mental neuropthy is a neurological manifestation of cancer and its metastasis that appears by the sensorial neuropathy of the mental nerve characterized by paresthesia or hypoesthesia of the lover lip, chin, oral mucosa and other regions which are supplied by the mental nerve branches. Its appearance is associated with an ominous prognosis. The aim of this review on numb chin syndrome is to explain the etiology, the pathogeny, the clinical characteristics and prognosis. Benign dental pathologies and iatrogenic maxillofacial complications are the most common cause of mental neuropthy. The most common malignancies that cause numb chin syndrome are breast cancer, lymphomas, prostate cancer, and leukemia. Numb chin syndrome may occur by the direct infiltration, perineural invasion, nerve compression, leptomeningeal involvement, and immune mediated mechanisms of the malignancies. Numb chin syndrome in neoplasia patients may indicate recurrence of the tumor, and is associated with an ominous prognosis. In a review, the mortality rate of the cases which have the symptoms of this syndrome was found 80%, with a mean survival of 7 months. Numb chin syndrome patients should be evaluated with investigations as orthopantogram, cone beam computed tomography, magnetic resonance imaging, bone scan, and positron-emission tomography-computed tomography. Additional investigations can be helpful in diagnosing the etiology in about 90% of malignant cases. The presence of mental nerve numbness symptoms requires careful examination of patients. Numb chin symptoms should be indicative not only for the bening factors but also for the presence of malignancy.