Three brothers with juvenile amaurotic idiocy were studied. Their symptomatology was dominated by three clinical manifestations: a - visual disturbances (progressive decrease of vision, ending, after few months, in total blindness) which were the first manifestation of the disease in all the cases and started at the age of 6 and 7 years; b - psychic disorders, which were evident in case 1, beginning at the same time of the visual impairment and persisting till the final stage of the disease (the patient died when she was 17 years old); the total impairment of the intellectual functions was also strongly marked in case 2 and less severe in case 3; c - convulsive seizures made their first appearance at the age of 11 years in all the cases. The somato-neurological examination disclosed only a generalized decrease of deep tendon reflexes (cases 1 and 2) and no extrapyramidal, cerebellar or pyramidal signs. The ophthalmoscopy showed, besides atrophy of the optic disks, pigmentar retinosis, which was evident in cases 2 and 3. The following studies carried out in cases 2 and 3 are particularly stressed: the examination of blood groups which showed marked consanguinity in the parents (first cousins); the electroencephalographic study; the electrophoretic determination of plasmatic proteins, lipo and glycoproteins, which evidenced significant changes in the three elements; the electrophoresis of the cerebrospinal fluid proteins, which showed decrease of the albumin/globulin ratio, specially dependent to increase of the γ fraction, in case 2 (the more severe); in case 3 it was only evidenced an isolated increase of the γ globulin, with fall of the β fraction. Finally, it was studied the vacuolization of the lymphocytes, found in high proportion in the peripheral blood of cases 2 and 3 and of their first cousin with similar disease; this feature seems to be correlated to the severeness of the disease.