We report on 2 patients with isochromosome 21q [i(21q)] or translocation 21q21q [t(21q21q)] in myeloid disorders. Of 18 available cases of i(21q) or t(21q21q), 15 were found in myeloid malignancies, often secondary to a previous carcinogen exposure. Complex karyotypes were found in most cases. Four cases presented with i(21q) or t(21q21q) as the sole anomaly, and this might represent a specific entity.