Three cases of the disease are reported by the author. Clinical observations showed them to be unilateral lesions, not affecting the Vth motor nerve fibers, and without any other neurological disorder. The lesions had been present for 16, 8, and 2 years respectively. Radiography and tomography of the petrous bone was normal, as was tomodensitometry in the third case. The three patient developed a syndrome with dysesthesia and hypoesthesia after several weeks or months, and this remained fairly constant. In such cases which progress over a long period of time, in which there is no anatomical basis, and in which no aetiology can be found, the only conclusions to be drawn are clinical ones: that this is a true syndrome of chronic isolated sensory neuropathy of the trigeminal nerve.