BACKGROUND We describe the case of a 74-year-old man diagnosed with primary cutaneous mantle cell lymphoma (MCL), an extremely rare and controversial condition that is not included in the World Health Organization-European Organization for Research and Treatment of Cancer classification for cutaneous lymphomas. CASE SUMMARY The patient presented diffuse cutaneous erythematous plaques and nodules throughout the body. Skin lesions were biopsied and histopathological examination showed diffuse monomorphic lymphocyte infiltration in the dermal and subcutaneous layers, sparing the epidermis. Immunohistochemical staining revealed CD20, cyclin-D1, CD5, and SOX-11 expression. Fluorescence in situ hybridization showed CCND1/IGH gene rearrangement. Correct diagnosis of primary cutaneous MCL requires ensuring that no other parts are involved; these cases require close follow-up to monitor their possible progression to systemic disease and for treating relapsed cutaneous disease. In this case, positron emission tomography scanning and clinical staging revealed no systemic involvement, and follow-up examination at 20 mo after diagnosis showed no evidence of systemic disease. The prognosis of primary cutaneous MCL is relatively good. Our patient received six cycles of chemotherapy, and the cutaneous manifestations presented almost complete remission. CONCLUSION Primary cutaneous MCL is rare, and its prognosis is relatively favorable. However, correct diagnosis is a prerequisite for proper treatment.