This study is focused on therapy-related myeloid neoplasms after the most promising frontline FCR (fludarabine, cyclophosphamide, and rituximab) therapy in previously untreated chronic lymphocytic leukemia patients. A total of 28 therapy-related myeloid neoplasm patients were identified, including 19 patients from 3 well-controlled FCR frontline trials (n=426 patients), giving an estimated frequency of 4.5% (1.9-8.3%) in a follow-up period of 44 months (range 5-122 months). Clinically, therapy-related myeloid neoplasms could emerge directly from 'prolonged myelosuppression' after FCR (10 patients), or after achieving complete hematological recovery (n=18). The overall latency was 35 months (range 3-118 months), with the former group of 23 months and the latter 42 months (P<0.001). In all, 10 cases presented as therapy-related acute myeloid leukemia and 18 as therapy-related myelodysplastic syndromes. Abnormal cytogenetics was present in 26 of 27 (96%) patients, with frequent chromosomes 5 and 7 abnormalities. The median survival was 7 months after therapy-related myeloid neoplasms. Our results indicate that the risk of therapy-related myeloid neoplasms secondary to frontline FCR therapy may not be as high as previously reported after removing the confounding factor of previous cytotoxic exposure, but this risk increased with older age and likely growth factor co-administration. Therapy-related myeloid neoplasms after FCR therapy shares clinicopathological features with therapy-related myeloid neoplasms secondary to other alkylating agents, but has a shorter latency interval indicating possible synergetic effects of the nucleotide analog fludarabine. The fact that therapy-related myeloid neoplasms can directly emerge from 'prolonged myelosuppression' warrants a bone marrow examination to rule out therapy-related myeloid neoplasms in this clinical setting.