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Even if reasons of autism spectrum disorders are not clear, there are many factors playing role in the autistic spectrum disorders, it is known that genetic factors have special importance. In recent years, genetic research of ASD has significantly increased. Like ASD, genetic factors have played a significant role in the etiology of schizophrenia spectrum disorder; environmental factors inşuence emergence of symptoms. Chromosomes 2, 7, 15, 16 and 22 are the most studied chromosomes to understand common genetic etiologies of these two disorders. Some genes on these chromosomes, such asNRXN1, CNTNAP2, APBA2, DOC2A, PRODH, PDZK1 DISC1are relatively important than others. In these case reports, we aim to draw attention to the importance of genetics in the etiology of ASD and schizophrenia. Case 1: A 14-year-old patient was brought to our child and adolescent psychiatry clinic for complaints of withdrawal and shyness. According to a medical history obtained from his mother; unwillingness to talk and to be involved with his friends, introversion and stuttering have been seen, when he was 9 years old. These complaints were increasingly worsened, as did his friendships and school lessons. During the examination, child said he did not want to go to school because, he was afraid that if he said something, his friends would tease with him. On the other hand, he did not want to leave the house. His communication with his family was getting worse. According to his first mental status examination, overall appearance was appropriate for his age. The patient was answered the questions without making eye contact. In addition, while he was talking, he looked down. When he stuttered, he got angry with himself and hit his own head with his hand. The patient had no problem with orientation, memory, caution and perception. His thought content and şow were normal. His answers were consistent with his psychosocial development. There was no specific feature in his past. Family History: His father has a congenital deafness; his sister has an ASD and his half-brother from his father’s previous marriage is schizophrenia. First, the patient was diagnosed with social phobia; also in the differential diagnosis, he was thought to have pre-psychotic process and prescribed sertraline 25 mg/d. During follow up examination when suspiciousness, visual and auditory hallucination as psychotic symptoms were observed, our diagnosis was changed as early onset schizophrenia and we discontinued Sertraline and Risperidone 1 mg/d was began. After the treatment, visual and auditory hallucinations and suspiciousness had disappeared. The negative symptoms continued. Medication and follow up of the patient is going on. In the past, it was thought that early onset schizophrenia and ASD were related syndromes even tough today it is accepted that they are separate disorders, Also research support common genetic basis of these disorders particularly related with parental heredity. We want to draw attention to genetic foundation of these disorders. The genetic research of this family of illnesses is going on.