Unfortunately there are no large randomized trials demonstrating the efficacy of olanzapine for CINV prevention in children receiving HEC. The positive experience with olanzapine reported in adult oncology patients has prompted some pediatric clinicians to prescribe olanzapine for individual children receiving chemotherapy. Olanzapine is frequently used for the treatment of schizophrenia and bipolar disorder in children and adolescents. Though various studies have demonstrated safety of olanzapine in children, data regarding the efficacy of olanzapine in children and adolescents for prevention of CINV is limited. There are many small studies describing the safety and efficacy of olanzapine for prevention of CINV. However, there are no large randomized trials. Olanzapine is available in generic form and is not an expensive drug. Therefore we would like to conduct a randomized trial to look for the efficacy of olanzapine in pediatric population for prevention of CINV