Primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL-LT) is a rare variant of the cutaneous B-cell lymphomas, with rapid growth and poor prognosis. Here, we report a case of PCDLBCL-LT on the foot in a senior woman. An 81-year-old woman presented with a rapidly growing mass on her left foot, and discoloration in both lower legs over the past 2 months was analyzed. Physical examination revealed hyperpigmented macules and papules on both lower extremities and a 3.0 × 2.0 × 0.5-cm, gray-dark nodule on the dorsal surface of the left foot. Histologic observation of the punch biopsy specimen revealed a sheet of atypical large centroblast/immunoblast-like lymphocytes; diffusely and evenly distributed in the dermis; with the immunophenotypes of CD45-positive, CD20-positive, Melan A-negative, Sox10-negative, S-100-negative, and CK20-negative; and a very high Ki-67 proliferative index (>90%). Further punch biopsy specimens of papules in the patient's lower extremities and bone marrow did not reveal atypical lymphoid tissues. Positron emission tomography/computed tomography did not show any metastatic lesions in distant organs and lymph nodes. The lesion was diagnosed as PCDLBCL-LT stage T1N0M0. The patient was treated with four cycles of combined therapy of rituximab and cyclophosphamide, hydroxydaunorubicin, vincristine (Oncovin), and prednisolone and the tumor was further treated with local radiotherapy. The tumor size was significantly shrunken. Primary cutaneous diffuse large B-cell lymphoma, leg type is a rare entity on the foot, characterized by a confluent sheet of diffuse large centroblast- and or immunoblast-like B cells with B-cell immunophenotyping. The combined therapy of rituximab and cyclophosphamide, hydroxydaunorubicin, vincristine (Oncovin), and prednisolone is the first-line treatment regimen, with increased survival.