We report a 79-year-old woman with primary cutaneous plasmacytoma in whom polymerase chain reaction (PCR) was used to demonstrate the monoclonality of the tumour, Four years after presentation, further sl;in lesions occurred and PCR again showed evidence of monoclonality despite the histology being non-specific. The reported frequency of multiple primary cutaneous plasmacytoma is increasing, sind the mortality rate of patients with multiple lesions is three times that of those with a solitary lesion, PCR may be a useful technique for assessing such patients at presentation.