Eleven married couples having histologically identical malignant tumors have been encountered: two couples with melanoma; three with carcinoma of the breast; two with carcinoma of the kidney, and one couple each with fibrosarcoma; carcinoma of the floor of the mouth; carcinoma of the colon and rectum, and carcinoma of the nasopharynx. The interval until the spouse of the patient with cancer was diagnosed to have cancer was within five years in all but three instances. The clinical course of the disease tended to be similar in both husband and wife. Generally, the longer the couple had been married, the more successful was their treatment. Those tumors described, as well as those identical cancers of husband and wife previously reported, have been suggested either experimentally or indirectly to have viral relationships.