Plasma cell proliferations represent a heterogeneous spectrum of disorders. A 7-year-old Caucasian female had suffered an asymptomatic eruption on the trunk for 4 years. Physical examination revealed a plaque with scattered red–brown papules and nodules. Chemical analysis revealed normal proteinaemia. Histological examination of biopsy specimens showed dense perivascular and periadnexal infiltrate, consisting largely of plasma cells, in the superficial and deep dermis. Immunohistochemical study showed that many cells of the infiltrate were CD20 positive. The plasma cells expressed κ and λ light chains. The girl’s status (age; absence of hypergammaglobulinaemia, lymphadenopathy and hepatosplenomegaly; presence of an infiltrate of mature polyclonal plasma cells restricted only to the skin) differed from those generally seen in diseases with plasma cell proliferation reported in the literature. This case seems unlike any other described up to the present time.