Background: hematological malignancies are one of the major causes of childhood morbidity;leukemia is the most common of pediatric cancers whereas lymphoma is the third most common childhood malignancy, NHL accounts for approximately 7% of cancers in children younger than 20 years. In patients with hematological malignancies the diagnosis of bone marrow involvement is important to determine prognosis and treatment protocols. MR imaging is the most sensitive imaging modality in the diagnosis of bone marrow infiltration and provides excellent details and additional accurate information about the extent of bone marrow involvement. Aim of the Work: this study aimed to evaluate the role of MRI in the diagnosis of different bone marrow lesions in pediatric patients with hematological malignancies with a trial to highlight the role of different recent modalities in the diagnosis, staging, monitoring management and in post treatment follow up of these patients. Patients and Methods: this study involved 63 patients (37 males and 26 females) with mean age of 9 years (range from 1.5 years: 16 years). They are cases of bone marrow biopsy proven hematological malignancy. They were categorized into two groups, group I: new cases who had bone marrow infiltration, they received no previous chemotherapy, group II: cases under follow up who have bone infarction, with history of chemotherapy or bone marrow transplantation (BMT). The MRI examinations were performed on a superconducting 1.5 T unit. Chi-square test was used to study the association between each 2 variables or comparison between 2 independent groups as regards the categorized data. The probability error at 0.05 was considered significant, while at 0.01and 0.001 were highly significant. Results: the different bone marrow lesions included in this study group of patients showed different MRI diagnostic criteria. A highly significant probability of errors was found in the relation between ADC values of bone infarction, bone marrow infiltration and red marrow.Conclusion: MRI provides an excellent imaging modality for the diagnosis of different bone marrow lesions is pediatric patients with hematological malignancies and can reliably differentiate between them based on the characteristic findings of each.