The following presents 6 cases of therapy related leukemia (TRL) along with discussion of their clinical features in comparison with those previously reported in Japan. Common primary malignancies were mammalian cancer, lung cancer and malignant lymphoma in both groups. It was observed that, 1) average age was higher (68 years), 2) average latent period from primary malignancy to leukemia was longer (10 years), particularly in patients treated solely with radiation, 3) in 4 out of 6 patients (67%) karyotype analysis of leukemia cells showed normal results, but in one case previously administered etoposide, translocation involving 15q+, 17q- was noted, and 4) the CR ratio in our cases was 83%; half the cases are still alive at 10 months of follow-up, while in previously reported cases the CR ratio was 41%, and the median survival time was 12 months according to Kaplan-Meier analysis. Although poor response to conventional chemotherapy has been reported in TRL patients, the present data indicated TRL in some cases to achieve complete response and long-term survival. Aggressive chemotherapy should be considered for such patients.