Dual-color interphase FISH was performed to B-cell Non-Hodgkin's lymphomas to detect numerical genetic alterations in c-MYC, RB-1, TP53 and centromere 8 and 17. The probe combinations c-MYC/centromere 8, RB-1/centromere 8 and TP53/centromere 17 were applied, and the hybridization signals scored in a correlated fashion. Copy number aberrations was found in 24 of 45 lymphomas examined (53%). Nine tumors (20%) had increased c-MYC gene copy number (three to 8 copies). Seven of these nine had increase in c-MYC copies relative to centromere 8 copy number. Allelic loss of RB-1 was found in 9 tumors (20%), one tumor lacked both alleles. Nine cases (20%) showed hemizygous TP53 deletion. TP53 deletion was significantly associated with high-grade histology (P = 0.02). Numerical alterations in c-MYC and RB-1 were not associated with prognosis. Patients with hemizygous TP53 deletion had shorter survival (relative risk = 6.1, P<0.001) than the ones with two or more alleles.