A patient with Philadelphia chromosome (Ph) negative acute lymphoblastic leukemia (ALL, FAB type L1) developed Ph-positive chronic myelogenous leukemia (CML) after more than 2 years in complete remission. Subsequently, Ph-positive lymphoblastic transformation occurred, which was again successfully treated. Thereafter, the CML state was interrupted twice more by blast crisis. The additional chromosomal abnormalities were atypical for Ph-positive CML. The course is interpreted as a possible example of the multistep development of CML. Blastic transformation occurring prior to the Ph chromosome has been reported in only two cases previously.