We report a case of common mantle cell lymphoma (MCL) with subcutis infiltration and transformation to blastoid MCL in the overlying dermis. The patient was initially diagnosed as having chronic lymphocytic leukemia and treated with chemotherapy. Eight months after the diagnosis of MCL with bone marrow involvement, subcutaneous nodules developed on the patient's left thigh and forearm. A skin biopsy showed a massive infiltration of neoplastic lymphocytes throughout the dermis and subcutaneous tissue. In the upper dermis, there was a perivascular mixed infiltrate of atypical large lymphoid cells and small-sized cells. In the mid to lower dermis, the infiltrate was dense with a nodular growth pattern and was composed of atypical large lymphoblast-like cells with large nuclei, dispersed chromatin, and numerous mitoses. In the subcutaneous tissue, there was a diffuse infiltration of neoplastic cells with common MCL cytologic features characterized by small- to medium-sized lymphoid cells. Cells in the common and blastoid variants of MCL were immunohistochemically positive for CD20 and cyclin D1 but negative for CD5. Neoplastic lymphocytes from the patient's bone marrow had the typical morphologic features and the immunophenotype of MCL (ie, CD5, CD20, cyclin D1, CD10, and CD23). Other case reports in the medical literature indicate that an MCL with skin invasion tends to have a poor prognosis. Our patient died 3 months after the appearance of skin invasion.