Three cases of Progressive Hypertrophic Neuritis are reported. The first refers to a sporadic case of the disease which began when the patient was 28 years old. The disturbances observed (muscular atrophies, thickening of peripheral nerves, loss of tendon reflexes and slight disorders of cutaneous sensibilities) and the absence of manifestations of tabetic or cerebellar type classify the case into the group of the simple hypertrophic neuritis. The atrophies commenced in the left hand and developed in a multiple and successive character. The second case also deals with a sporadic form of the disease with essentially peripherical symptomatology (simple form of the N.H.). The illness started at 18 years of age; no familial incidence; the muscular atrophies occurred in a multiple and successive manner beginning in the left leg; the signs of the tabetic or cerebellar group were absent. The third case refers to a patient in whose family numerous references to neurological disturbances are encountered. The case studied (IV-3) and one of the sisters of the patient (IV-6) and probably the other indicated members of the family present essentially an amyotrophic picture associated to the signs of the tabetic group. The thickening of the peripheral nerves was verified in cases IV-3 and IV-6, thus establishing the diagnosis of hypertrophic neuritis, Déjerine-Sottas' form. The research of thickening of nerves unfortunately could not be investigated in the other members of the family. In case 3 the disturbances commenced at approximately 40 years of age, differing from the classic cases of Déjerine beginning in childhood or adolescence. A biopsy of superficial branch of the radial nerve was performed in cases 1 and 2 and the histopathological examination revealed the characteristic lesions of "schwannite hypertrophique" ("onion bulbs"). The principal elements concerning the historical of the disease, symp-lomatology, clinical forms and diagnosis are described later. The cardinal feature of the disorder (amyotrophies, thickening of peripheral nerves, loss of tendon reflexes) and the associated symptoms and signs (sensory, ocular, cerebellar, trophic changes, etc.) are analysed. Regarding the clinical forms, the author distinguishes: 1) the simple forms, or purely neuritic, characterized by the progressive amyotrophy of distal limb segments, thickening of peripheral nerves, loss of tendon reflexes and impairment of cutaneous sensibility; and 2) the complete or combined form, in which the disorders of tabetic or cerebellar group add to those previously referred to. While the sporadic cases of H.N. generally assume the first form, the familial cases, beginning in childhood, usually reveal the second form. It seems that the diseases is sometimes not recognized, confused with amyotrophic and ataxic syndromes of another nature, because the research of the enlargement of peripheral nerves is not always accomplished in the habitual neurological examination.