A patient who had primary gastric B-cell non-Hodgkin's lymphoma, invasive ductal breast cancer and a basocellular carcinoma of the forehead in her medical history was studied. Three years after polychemotherapy and irradiation of the breast cancer, a rapidly enlarging, ulcerated violaceous tumour developed on the patient's left leg. The tumour was identified by the histopathological, immunohistochemical and immunoglobulin gene rearrangement analyses as a cutaneous large B-cell lymphoma. No signs of extracutaneous involvement were detectable. Despite surgical excision, interferon-alpha2b treatment and chlorambucil + prednisone chemotherapy, a relapse occurred in the previously affected site, whereafter the patient received radiotherapy. She was lost to follow-up, and died approximately 14 months after the surgical intervention without autopsy. We discuss the clinical and histologic features and outcome of the large B-cell lymphoma of the leg, its coincidence with other diseases, and the uncommon occurrence of primary multiple malignant tumours.