NOTCH1 mutations occurred in 5/52 CLL cases (10%), in which a preferential association with IGHV unmutated clones (80%, P = 0.02) and a high frequency of cases (3/5, 60%) harbouring trisomy 12 as an additional isolated chromosomal abnormality (P = 0.007) was observed; in the remaining two CLL cases, the presence of NOTCH1 mutation was associated with del(13q14) involving the RB1 gene and to both del(13q14.3) and del(17p), respectively. The gene discussed is NOTCH1; the disease is B-cell chronic lymphocytic leukemia.