Merkel cell carcinoma (MCC) is a rare and aggressive primary neuroendocrine carcinoma of the skin. Large tumours, in particular, show rapid progression and metastatic dissemination, while smaller tumours show less aggressive behaviour. Cyclin A is considered to play a central role in cell cycle control. Its overexpression has been found to correlate with prognosis in many types of carcinomas and sarcomas. Twenty-six MCC patients with complete clinical data were selected. Formalin-fixed paraffin-embedded primary tumour samples were immunohistochemically stained for cyclin A. Correlation between expression of cyclin A and primary tumour size, invasion of subcutaneous tissue, local recurrence, metastasis and survival was statistically analysed. Twenty-five samples expressed cyclin A, and the mean value of positive cells was 25%. Our findings demonstrate that even small and superficial MCC show overexpression of cyclin A. There was no statistical correlation between cyclin A expression and the above-mentioned variables. Cyclin A does not seem to be useful as a prognostic tool. Consequently, size of the primary tumour (>/=2 cm) remains the primary prognostic tool. As a result every tumour, even those small in size, should be considered aggressive and treated radically and rapidly.