We describe a case of acute myeloid leukemia in a 2 1/2-year-old boy presenting with a mediastinal tumor causing respiratory distress, and lymph node enlargement in the cervical and inguinal regions. Apart from myeloid markers CD13 and CD33, blast cells also expressed stem cell marker CD34 and megakaryocytic marker CD61. Cytogenetically, inv(7)(p21q31) was found in 9/25 and 15/25 analyzed metaphases from short-term cultures of lymph node and bone marrow cells, respectively. The patient is in continued complete remission 26 months post diagnosis. The case demonstrates that chromosome aberrations other than inv(16), t(8;21), and t(9;11) may be associated with extramedullary disease, and that not all chromosome 7 aberrations are prognostic adverse findings.