Background Cytomorphological assessment of erosive skin tumours offers a rapid and minimally invasive way to obtain a diagnosis. However, the studies so far conducted on this method have been relatively small. Aim To conduct a large retrospective study on cytomorphological assessment of erosive skin tumours. Methods In this study, 86 cytological smears prepared from erosive cutaneous tumours clinically suspicious for melanoma were examined to test the diagnostic accuracy and practicability of cytomorphological evaluation of such tumours, and to compare the assessments of two investigators with different experience levels. In a subgroup of tumours, cytological assessment was compared with dermoscopic evaluation. Results There was agreement in the cytological and histopathological results for 68 of 86 cases (79%) assessed by the experienced investigator and in 64 of 86 cases (74%) assessed by the inexperienced investigator. The diagnosis was confirmed cytologically in 39 and 34 of 42 melanomas, and in 28 and 27 of 35 basal cell carcinomas, respectively. The sensitivity of the cytodiagnosis was not significantly different between the two investigators. The dermoscopic evaluation showed good agreement with the cytological results for melanoma (82.4%), although use of dermoscopy was only possible for 49.9% of the lesions because of difficulties with the samples. Conclusions Cytological assessment of erosive melanoma and BCC lesions is a useful tool for gaining additional information on clinically uncertain skin tumours, and shows good agreement between different investigators.