We report a case of primary multiple cutaneous plasmacytomas, without underlying multiple myeloma, treated with intralesional tumour necrosis factor-alpha (TNF-alpha). A marked reduction in tumour size, with no significant adverse effects, suggests that intralesional TNF-alpha is an effective treatment for non-solid malignant tumours. Extramedullary plasmacytoma, especially involving the skin as a primary site, has rarely been reported in the English literature. We describe the ninth reported case of multiple cutaneous plasmacytomas without underlying multiple myeloma. Intralesional tumour necrosis factor-alpha (TNF-alpha) was used to treat this disease and its anti-tumour effect quantitatively evaluated by comparing the tumour size and histological change before and after treatment.