This report is based on a review of the present situation of the sudden infant death syndrome through the presentation of four cases studied at the Unidad de Pediatría, Hospital General de México, S.S.A. All cases were in apparent good health before death. All babies were less than ten months of age. In three cases, necropsy was not performed, and the other one did not show significant abnormalities at the post-mortem examination. A complete review of the literature was made including: historical, epidemiological, genetic, clinical and pathological aspects. Special emphasis is made on the pathophysiology of the syndrome during MOR phase of sleep and muscular hypertrophy of the lungs arteriolae suggesting chronic hypoxia which are the most relevant theories in the sudden infant death syndrome. Psychological aspects and the family management by the physician and detection of possible future victims of the syndrome are finally discussed.