Secondary acute leukaemia (s-ALL) is a destructive complication in patients who have been previously treated for other cancer. Secondary acute lymphoblastic leukaemia is rarely reported whereas secondary acute myeloid leukaemia is much more common. Chromosomal 11q23 abnormality, frequently detected in therapy-related acute myeloid leukaemia, is the most common cytogenetic alteration in secondary ALL too. However, s-ALL cases without 11q23 abnormality have rarely been described. Furthermore, there are only a few published medical reports describing occurrence of acute lymphoblastic leukaemia in multiple myeloma (MM) patients. We would like to present our experience with a patient with MM, who developed ALL without 11q23 abnormality, nine years after alkylating-agent containing treatment. The course of the disease was complicated by thrombosis that obstructed the possibility of effective treatment. In conclusion, it should be kept in mind that the development of a more aggressive neoplasm related to chemotherapy treatment as well as the inherent genetic instability of normal and abnormal lymphoid progenitors may affect overall survival of an indolent lymphoma patient.