The authors emphasize the importance of the occipito-cervical malformations in the determination of several neurological pictures. The differences between platybasia and basilar impression are stressed. Particular reference to surgical and orthopedic treatments is made. The authors consider the clinical diagnosis and discuss the worth of the radiological indices proposed by Chamberlain, McGregor, and Fischgold and Metzger, and the usefulness of contrasted radiographies (iodized oil myelography and ventriculography). Twelve cases of marked and 7 of slight basilar impression, and one of possible "manifestation of occipital vertebra" are reported; occipitalization of atlas coexisted in 9 cases, and Klippel-Feil syndrome in 4; other malformations were also present (rachischisis, cervical kyphoscoliosis). The authors comment on the neurological symptomatology, which simulated various clinical pictures, mostly cranial nerve palsies, syndromes of pyramidal, sensory and cerebellar pathways, signs of lateral amyotrophic sclerosis and syringomyelia. The examination of cerebrospinal fluid, performed in 18 cases, showed protein-cytologic dissociation in 5 and spinal block in 3. Discussing the radiological features, it is emphasized that the distance between the tip of odontoid and the Fischgold and Metzger's line prevailed on the distance between that point and the Chamberlain's line; there was no statistical correlation between both distances, a finding that does not invalidate any of these indices, only stressing the need of they being analysed in conjunction and on the light of the clinical manifestations. The clinico-radiological correlation was not statistically significant; however, the occipitalization of the atlas has strongly prevailed in the cases of severe neurological symptomatology. The results of surgery in 3 cases are analysed in detail.