To date, 85 cases with unusual Ph1 translocations have been described and are summarized in the present work. Of the 85 translocations, 41 were simple and 44 complex. Only chromosomes #1, #4, #8, and #20 and the Y have not been found to be involved in simple translocations and #12, #16, #18, #20 and the Y in complex ones. Chromosomes #18, #20, and Y have not been involved to date in either complex or simple Ph1 translocations. Four cases have been reported in whom more tan three chromosomes were involved in the Ph1 translocation and only four cases in whom the #9 was not involved in complex Ph1 translocations. The chromosomal changes, in addition to the Ph1, accompanying unusual Ph1 translocations in CML are not different from those seen in cases with the standard type of Ph1 translocation. Translocations (other than the Ph1) in CML occur in less than 1% of the cases and, to date, have found to involve all the chromosomes except the X and Y. With rare exceptions, in complex Ph1 translocations 1) the distal end of #22 is translocated to a third chromosome (i.e., other than #9), a part of which is translocated to #9, #2) the breaks in the involved chromosomes probably occur concomitantly, and 3) a characteristic PH1 chromosome is present. The survival of patients with CML and unusual or complex Ph1 translocations does not differ significantly from that of patients with the standard Ph1-translocation.