Ewing sarcoma of the bones, extraskeletal and peripheral primitive neuroectodermal tumors all belong to the Ewing sarcoma family of tumors. Ewing sarcoma is the second most common primary malignant bone tumor in older children and young adults following osteosarcoma. Pelvic bones, the long bones of lower extremities, as well as the thorax and soft tissue of the above mentioned locations are often affected. They often metastasize into the lungs, bones and bone marrow, but rarely into the nodes, the liver and the brain. Ewing sarcoma was only sporadically reported from different organs. Specific chromosomal aberrations affecting chromosome 22 - translocation t(11;22), fewer t(21;22), and the rarely occurring so-called minor translocation - are typical of Ewing sarcoma. Translocations, specific for the Ewing sarcoma family of tumors combine a part of the EWS gene, localized on chromosome 22, with some of the ETS family of genes (FLI-1, ERG, ETV-1 and others). Besides these specific translocations in Ewing sarcoma secondary changes are revealed, such as trisomy and tetrasomy of chromosome 8 and 12 and often nonbalanced translocation t(1; 16) leading to deletion of 16q and amplification of 1q. The significance of establishing these secondary aberrations for prognosis is the focus of intensive research. However, t(1;16) translocation and trisomy or tetrasomy of chromosome 8 are appear to be indications of unfavorable prognosis of the disease.