Second malignancies represent an important iatrogenic complication of the treatment of hematologic and other neoplasms. In this review we summarize the literature relating specifically to malignancies developing in the wake of treated non-Hodgkin's lymphoma (NHL). In these patients, the risk of myelodysplastic syndrome (MDS) and acute non lymphocytic Leukemia (ANLL) is reported to be increased 10–105 fold over that of the general population. Factors in the development of MDS and ANLL include basic defects in cellular immunity in NHL patients as well as treatment with alkylating agents and low dose total body irradiation. Biologically these secondary MDS and ANLLs are characterized by specific cytogenetic abnormalities and results of treatment are poor. Currently bone marrow transplantation offers the only potential cure.There is no clear statistical evidence that solid tumors occur more frequently after NHL. However, bladder carcinoma, in cyclophosphamide treated patients, and lung cancer have been reported by some to occur with an increased incidence. Further investigation of the molecular events leading to the occurrence of second malignancies in NHL patients and the role played by oncogenes and tumor suppressor genes in this process is still needed.