Feline mammary carcinomas (FMC) were surgically resected from 51 cats to verify that the nucleolar organiser regions (AgNORs) count is related to the post-surgical survival time (PST). After one year post-surgery, 27 cats (group A) were still alive (52.9 per cent) while (41.7 per cent) (group B) had died as a consequence of FMC. Formalin-fixed, paraffin wax-embedded histological sections were stained with silver nitrate and the AgNORs were then counted at x 100 oil immersion objective. In FMC AgNORs count ranged from 1.2 to 12.1 (6.10+/-2.3). A statistically significant difference (P=0.000112) in the AgNORs count was found between cats from group A and group B. No other statistically significant differences were found between group A and B. AgNORs count was not correlated to age or different histological type, according to the WHO classification. Using this technique it is possible to identify two populations of FMC with a statistically significant difference in the PST.