In this study we evaluated the behaviour of proliferating cell nuclear antigen labelling index (PCNA‐LI), mitotic index (MI) and histological features in ten basal cell carcinomas (BCC) and ten squamous cell carcinomas (SCC) of canine skin. PCNA‐LI ranged from 2.1% to 4.8% in SCC and from 0.1% to 2.0% in BCC samples. A significant statistical correlation, between PCNA‐LI and MI could be demonstrated only in SCC, but not in BCC samples. Furthermore, PCNA‐LI was also significantly and consistently greater in the three BCC of solid type and in poorly differentiated SCC. PCNA‐LI may provide additional criterion in evaluating the intrinsic malignancy and growth potential of the above tumours.