BACKGROUND Clinical Features of double cancers associated with renal cell carcinoma (RCC) detected at the clinical course, especially focusing on the comparative analysis between the male and female patients, were unknown. From this background, we tried to search for clinical characteristics of double cancers associated with RCC. METHODS The eight hundred and four patients with RCC have been treated at our University Hospitals and affiliated hospitals, and of them, the 38 patients (male in 25, female in 13) had double cancers during the clinical course, and these patients were objective in our study. RESULTS 1) When we looked at all patients, there observed gastric cancer most frequently in 14 (36.8%), lung cancer in 3 (7.9%), prostate cancer in 3, bladder cancer in 3, uterine cancer in 3, rectal cancer in 2 (5.3%), thyroid cancer in 2, and pharynx, esophagus, T-cell lymphoma, chronic lymphatic leukaemia (CLL), renal pelvis, sigmoid colon, brain and colon cancers in 1 (2.6%) respectively. 2) As to the male patients, there observed 10 gastric cancers, of them, 2 died of this disease (20%), 3 lung cancers, of them, 2 died of this disease (66.7%), 3 prostate cancers, of them, 2 died of this disease (66.7%), 3 bladder cancers, of them, 1 died of this disease (33.3%), and 1 cancer patient with pharynx died of this disease, esophagus, T-cell lymphoma, CLL, renal pelvis and sigmoid colon died of this disease. Regarding the female patients, there observed 4 gastric cancers, all of them died of this disease, 3 uterine cancers, all of them died of this disease, 2 rectum cancers, all of them died of this disease, 2 thyroid cancers, of them, 1 died of this disease, 1 brain cancer and 1 rectal cancer. Furthermore, as to the timing at the detection of double cancers during the clinical course, the 10 patients (40%) detected double cancers simultaneously in male patients. On the other hand, no patient with double cancers was detected simultaneously in female patients. CONCLUSIONS The gastric cancer is most frequently observed as double cancer in both of male and female patients with RCC. But, in the female patients, it shows more frequently died of double cancers associated with RCC compared with those in male. Furthermore, as to the timing at the detection of double cancer is asynchronous in all female patients with RCC.