Ewing sarcoma is the second most common malignant bone tumor in children and young adults. FISH analysis to identify a common translocation t(11;22)(q23;q12) or less frequently t(21;22)(q22;q12) or t(7;22)(p22;q12), plays an important role in the confirmation of clinical diagnosis. The translocation t(11;22)(q24;q12) has been detected in both fresh tumor cells derived by biopsy of primary & metastatic tumors as well as in cell lines established from patients with Ewing sarcoma. It is found in 90–95% of patients with Ewing sarcoma. FISH can detect this rearrangement in interphase cells only.