Stable maintenance of chromosomes needs the functional telomeres at the chromosomal ends. It has been proposed that the loss of telomeric function (LTF) plays a major role in the production of abnormal chromosomes, such as the telomere association (TA) and the jumping translocation (JT). We analyzed TA and JT to evaluate the involvement of LTF in chromosomal instability. A shortened telomeres was identified at the fusion point of the JT. We also developed a method to examine TA based on PCR and found relationships between telomere shortening and products of PCR. Our findings strongly suggest that LTF may cause chromosomal instability and contribute to cancer cell evolution.