Eight canine cutaneous adenomas and eight canine cutaneous carcinomas were analysed by computer-assisted nuclear morphometry in Hemacolor-stained cytological specimens. In each case, the nuclei of at least 100 neoplastic cells were measured, and the mean nuclear area (MNA), mean nuclear perimeter (MNP), mean nuclear diameter (MND) and nuclear roundness (NR) were calculated. The results indicated an increase in the mean values of investigated parameters from canine cutaneous apocrine adenomas (MNA, 75.65+/-2.22; MNP, 31.05+/-0.55; MND, 9.62+/-0.14; NR, 1.10+/-0.009) to canine cutaneous apocrine carcinomas (MNA, 88.78+/-11.29; MNP, 34.38+/-2.43; MND, 10.43+/-0.76; NR, 1.21+/-0.07). The statistical analysis revealed statistically significant differences between benign and malignant neoplastic cells (P<0.01). The statistical differences between investigated parameters (P<0.01) were also found between the metastasizing apocrine carcinomas and all other examined carcinomas. The results indicated that the computerized morphometry could be used as an effective auxiliary tool for differential diagnosis between canine cutaneous adenomas and carcinomas on cytological smears.