A 56-year-old man with chronic myelogenous leukemia (CML) who presented with a variant Ph chromosome, t(5;9;22)(q13;q34;q11), developed a unique additional chromosomal change of a double reciprocal t(1;7)(p36;p11) during the accelerated phase. A minor clone that had two copies of 1p+ and a copy of 7p− with a normal chromosome 7 was observed simultaneously. The patient underwent a megakaryocytic crisis. Surface marker of the blasts was positive for CD13, CD33, HLA-DR, CD41a, and CD42b, and negative for CD14 and lymphoid markers. Sequential chromosome analysis suggests that the double t(1;7) was caused by a multistep event consisting of duplication of both derivative chromosomes accompanied by loss of normal chromosomes 1 and 7. This may be the first report of a double reciprocal chromosomal translocation in a hematopoietic neoplasm.