Abstract: The patient was a 41-year-old man,who presented with painful,pruritie and infiltrated plaques in the gluteal region for more than 3 months.Skin examination showed brunneus,egg-sized,infiltrated plaques in the right gluteal region surrounded by irregularly sized,mildly infiltrated and dark erythematous patches.Histopathological examination revealed a diffuse,clump- or patch-like inflammatory cell infiltrate predominated by mature plasma cells mixed with lymphocytes and histiocytes,which extended into the fat tissue.No mitosis was observed.Neither acid-fast nor periodic acid-Schiff (PAS) stain was positive.Immunohistochemistry showed positive staining for CD138, and λ chain.Laboratory examination showed that the concentration of immunoglobulin κ chain was 1570.00 mg/dl in sera and 3.8 mg/dl in urine,while that of immunoglobulin λ chain was normal in both sera and urine.Urinary Bence-Jones protein was negative.Serum protein electrophoresis showed that the level of γ-globulin was 24.60.Bone marrow biopsy showed no abnormality.He was finally diagnosed with cutaneous plasmacytosis.After managed with surgical resection as well as oral triamcinolone and thalidomide,the lesional infiltration and area decreased.