Acute promyelocytic leukemia (APL) is considered as a curative disease after combined chemotherapy based on all-trans retinoic acid (ATRA) and anthracycline. However, as long-term survivors continue to increase, reports on sporadic cases of therapy-related myeloid neoplasm (t-MN) after successful APL treatment are also increasing. Recently, we have experienced one patient who developed t-MN 7 yr after APL diagnosis. Even though he had not been exposed to alkylating agents at all, he showed alkylating agents-associated features such as long latency period (>5 yr), first presentation as myelodysplatic phase (multilineage dysplasia with increased blasts), and complex karyotype including monosomy 5 and 7. He received only supportive care and expired 3 months after the diagnosis of t-MN (6 months of survival after the onset of cytopenias). t-MN after complete remission of APL is a rare but fatal complication, and patients with complex karyotypes show ominous prognosis in particular. For the early diagnosis of t-MN, long-term and close monitoring of the patient is needed. One should suspect this late complication whenever any unknown cytopenia develops, and should perform bone marrow biopsy and cytogenetic analysis.