Secondary leukemia refers to a unique category of myeloid leukemia which develops secondary to cytotoxic therapy or MDS or environmental carcinogens or radiations. Transformation of myeloproliferative neoplasm on therapy has been excluded from this category. Therapy related leukemias, constitute a major subgroup which occurs as a late complication of cytotoxic therapy of both malignant and non malignant disorders. The most common (approximately 70–80%) among these are secondary to alkylating agents or radiations effect, usually characterized by unbalanced chromosomal translocation. A smaller group (20–30%) is secondary to treatment with topoisomerase inhibitors and usually associated with balanced chromosomal translocation. The latency period very from 1–10 years. Therapy related acute myeloid leukemias (t-AML) and therapy related MDS (t-MDS) are more common. Acute lymphoid leukemia, CML and CLL are rare. The outcome of adults with t-AML is not significantly different from de novo AML when data is adjusted for cytogenetic risk groups. However, more studies are required in this field.