A case of primary cutaneous CD30(Ki-1)-positive pleomorphic large cell lymphoma in a 51-year-old woman with generalized lichen myxedematosus is presented. Histopathological findings of the biopsy specimens from the lichenoid papules of the left forearm and the dorsum of the right hand were compatible with papular mucinosis. The mucinous material in the papillary dermis stained with alcian blue at pH 2.5 and was susceptible to hyaturonidase, but serum protein electrophoresis showed no abnormal bands and an abnormal paraprotein was not detected in our patient. Histopathological examination of a solitary, firm, purplish nodule on the right popliteal area showed diffuse and extensive infiltration in the reticular dermis composed of large, atypical, often hyperchromatic, sometimes multinucleated and markedly pleomorphic cells. The majority of the large atypical cells were CD30(Ki-1) positive. The TCR gene re-arrangement analysis demonstrated the presence of a monoclonal rearrangement of the y-TCR gene in the skin biopsy specimen of our patient. The organ-system survey revealed no evidence of internal organ involvement. We concluded that this was primary cutaneous CD30(Ki-1)-positive pleomorphic large cell lymphoma developing in a patient with generalized lichen myxedematosus.