We report a case of pre-B-cell acute lymphoblastic leukemia (ALL) with the Ph1-chromosome, t(9;22) translocation and P190 associated BCR/ABL rearrangement. One cell with the Ph1-chromosome and t(9;22) also had del(5q). Interestingly, another diploid cell with iso(17q) lacked the Ph1-chromosome and t(9;22). This finding, similar to one reported in chronic myelogenous leukemia, is consistent with the possibility that abnormality manifest as chromosome instability antedates the Ph1-chromosome and t(9;22) in some cases of Ph1-chromosome positive acute leukemia.