Therapy related acute lymphoblastic leukemia (t-ALL) of B cell origin is rare and constitutes approximately 2% of all ALL. Previously compiled data on the complete cytogenetic analysis of 48 t-B-ALL cases suggested that MLL rearrangement at 11q23 gene locus is the most common abnormality. Philadelphia chromosome (Ph) and a normal karyotype were reported as the second and third most common karyotypes, respectively. We investigated cytogenetic karyotypes of six t-B-ALL cases with a pre-B cell immunophenotype. Ph + t-B-ALL was noted in four of six patients previously treated with radiation and/or chemotherapy. In addition, one case demonstrated MLL rearrangement at 11q23 locus while one case demonstrated normal cytogenetic karyotype. Five of the six t-B-ALL patients had persistent leukemia following initiation of chemotherapy for secondary leukemia with survival ranging from 10 to 21 months. To our knowledge, only fourteen patients with Ph + t-B-ALL have been described in the literature. In the current study, three of four cases with Ph + t-B-ALL were associated with treated breast carcinoma while one patient was treated for Hodgkin lymphoma. All four patients had undergone radiation therapy. The results may indicate a plausible association between Ph+t-B-ALL and prior radiation exposure.