Aplastic anemia (AA) is marrow failure due to an inadequate number of hematopoietic cells in the marrow. Prior reports have described a more aggressive clinical course in aplastic anemia with monosomy 7. We report 3 pediatric cases of AA with normal cytogenetics followed by acquisition of monosomy 7. Bone marrow biopsies were initially diagnostic of AA but later showed monosomy 7 and an increased number of megakaryocytes with small hypolobated nuclei. Immunohistochemical stains for CD61 highlighted the marked dysmegakaryocytopoiesis. The marrow blast percentage was increased in only 1 patient with 4.6% blasts. The 3 patients underwent bone marrow transplantation, and each has remained disease free for 7 to 18 months after transplantation. Pediatric patients with AA and normal cytogenetics may develop monosomy 7 with a myelodysplastic syndrome, unclassified. Patients with AA and monosomy 7 should be evaluated for dysmegakaryocytopoiesis.