Schizophrenic monozygotic twins concordance  is of only 45% although both twins share 100% of the derived genoma of a single zygote for what the discordance in monozygotic twins is related to the influence of prenatal environmental factors independently of genetic factors. These prenatal environmental factors are related to the alterations in the brain and  the skin more frequently observed in patients since both tissues are derived from the embryonic ectoderm. This fact explains the anomalies of the nervous system together with anomalies of the hair, face, hands and feet more frequently observed in schizophrenics discordant twin than in the normal population. Among the  environmental factors virus occupies a more and more excellent position for the results obtained in clinical observations in human and in experimental animals. A virus acting in this first phase of  development, especially during the 2do. pregnancy trimester can explain the anomalies observed in both structures derived of the embryonic ectoderm in the affected twin. In the present work the results obtained in an ultrastructural study are exposed in samples of the brain of two monozygotic twin fetuses with strong antecedents of schizophrenia in their family. The obtained findings indicate an infection for the virus herpes simplex hominis type I [HSV1] in the brain of one of the twins and mitochondria alterations. The obtained results can explain the discordance of the illness found in the postnatal clinical and epidemiologic studies. It should be considered their relation to the viral etiology to be the first direct evidence of virus in the brain of a fetus from a schizophrenic mother with important biological load of family schizophrenia.