Three cases of malignant lymphoma (ML) accompanied by renal cell carcinoma (RCC) are reported. From September 1997 through August 2000, we treated 85 patients with ML. Among these patients, three had accompanying RCC (clear cell type): case 1, a 57-yr-old man with gamma/delta-T cell lymphoma; case 2, a 25-yr-old man with Grade 3 follicular lymphoma; case 3, a 64-yr-old man with MALToma of the right orbit. Renal cell carcinoma is a relatively rare disease, but several reports have indicated that, for some reason, the incidence of concurrent RCC and ML is higher than expected. It is possible that the two malignancies share some common background factors, such as genetic mutation, immunological abnormality, or an immunomodulatory effect of the first tumor. The patient in case 2 was thought to have an abnormal immunological background from his medical history, which included bronchial asthma, idiopathic thrombocytopenic purpura, and mesangial proliferative glomerulonephritis (non-IgA type). Therefore the combination of ML and RCC in this patient may have been due to immunological impairment.