Chromosome banding studies performed on 106 cases of CML in Sapporo revealed that 101 (95.3%) were Ph1-positive, and 5 (4.7%) Ph1-negative, the latter including a case of juvenile type CML. Of the 101 Ph1-positive patients, 98 showed the standard type Ph1 translocation, t(9;22)(q34;q11), while the remaining 3 had a complex Ph1 translocation as represented by t(4;9;22), t(9;14;22), or t(9;10;15;19;22). There were 28 patients who showed other chromosome changes in addition to the Ph1 translocation. Trisomy 8, duplication of Ph1, isochromosome 17q, and trisomy 19 were most frequently involved in the additional changes, and 2 or more of them often participated in the major routes of karyotypic evolution. Other additional changes observed were 6 translocations, 4 partial deletions, 2 partial trisomies for 1q, trisomies 6, 7, 12, 15, and 21, a monosomy 5, a partial duplication of no. 9, a missing Y, and so on.