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Schizophrenia is a serious mental disorder emerging at early ages, characterized by significant breakdowns in thought, perception and behavioral processes, alienation to common manners of perception and interpretation, a unique type of isolation and withdrawal from human relations. It is defined as very early onset schizophrenia (VEOS) when the symptoms occur before the age of 13; and as early onset schizophrenia (EOS) when they occur before the age of 18. Psychopharmacologic and psychosocial approaches should be combined for the treatment of schizophrenia. Although the effects and side effects of both typical and atypical antipsychotics from the field of psychopharmacology have been studied for adult patients in detail, the studies made for child and adolescent age group are inadequate. Children and adolescents are more susceptible to side effects than the adults. Atypical antipsychotics have been proven to be more efficient on negative and cognitive symptoms compared to typical antipsychotics. Clozapine is a prototype of atypical antipsychotics and the first antipsychotic to be defined as atypical. Clozapine is a HT2A/D2 antagonist. Clozapine is effective on cases, on which typical and other atypical antipsychotics having the most efficiency yet the most side effects fail, and is accepted as “gold standard” in the treatment of schizophrenia. The most serious side effect of the drug is agranulocytosis, which may cause death and are observed approximately 1% of the cases. The risk of seizures increases especially in high doses. In addition it may cause intensive sedation, hyper-salivation, weight gain and myocarditis. In this paper, the effects and side effects of clozapine in five adolescent cases diagnosed to have VEOS and EOS are discussed. The clinical evaluations of the cases during the process have been made as follows: the side effects have been assessed with Extrapyramidal Symptoms Rating Scale (ESRS); the severity of the disorder has been assessed with “Clinical Global Impression Scale/Severity” (CSI-S); improvement rate during the observation process has been assessed with “Clinical Global Impression Scale/Improvement” (CSI-I); level of functionality has been assessed with “Global Assessment Scale” (GAS); and the psychotic symptoms have been assessed with “Scale for the Assessment of Negative/Positive Symptoms” (SAPS/SANS). Four cases showed a quite good response to the treatment and tolerated clozapine, the last case (Case IV) showed apparent decreasing trend in neutrophil count. In this case report, evaluates the efficiency and the side effect profile of clozapine treatment on five adolescent cases in total, one case with VEOS diagnosis and four cases with EOS diagnosis. The clinic examination results of four cases (Case I-II-III-V) showed that clozapine is effective on childhood schizophrenia. While these four cases showing a quite good response to the treatment tolerate clozapine well, the last case (Case IV) showed apparent decreasing trend in neutrophil count a short while after starting the treatment and consequently the treatment was stopped. Follow-up process and other findings were discussed accompanied by the literature.