Specific inhibition of expression of a fusion gene in mammals occurs using a short, double-stranded ribonucleic acid molecule (dsRNA). The dsRNA comprises two separate non-linked RNA strands, an 51 strand and a complementary strand. The strands are 20 to 23 nucleotides in length, and the 51 strand is complementary to the fusion junction of the AML-1/MTG-8 fusion gene. The dsRNA also comprises at least 3 nucleotides on each side of the fusion junction. The dsRNA can be introduced into and maintained in a mammalian cell under conditions and for a time sufficient to obtain degradation of mRNA of the fusion gene to inhibit expression of the fusion gene. The dsRNAs and methods described are useful for treating diseases caused by chromosomal aberrations, particularly malignant diseases such as lymphoma and leukemia.