Sixty eight CLL patients with isolated del(13q) detected by CLL FISH panel (ATM, TP53, 13q14 and trisomy 12) between 2006 and 2019 were included in our study, in which we aimed to investigate the cause of the clinical heterogeneity of CLL cases with del(13q). Here, ATM is linked to B-cell chronic lymphocytic leukemia.