BACKGROUND. Nasopharyngeal carcinoma (NPC) and anaplastic salivary gland carcinoma (SGC), both associated with Epstein-Barr virus (EBV), are common among Inuit from Greenland, Canada, and Alaska. Because immigrant studies have shown that factors acting early in life are important for the development of NPC, the authors interviewed new patients in Greenland with either NPC or SGC about their lifestyles during childhood and additional cases in their families. METHODS. On admission, new patients from Greenland with either NPC or SGC were interviewed about childhood life-style, family size, and other cases of NPC or SGC within the family. Additional cases were confirmed by review of the medical records concerning these patients. RESULTS. During the 11 years from 1980 through 1990, 17 of 63 (27%) cases in Greenland were found in familial clusters among first-degree relatives. There were no differences in the life-styles of multiple-case families and single-case families. CONCLUSIONS. The high rate of familial clusters among natives of Greenland is of interest because EBV is believed to play a role in the origin of these two diseases similar to that of Marek disease in neurolymphomatosis of chickens. Therefore, the familial clustering of NPC and SGC may indicate that an enhanced oncogenic potential of an EBV strain may occur more frequently in Greenland than in other parts of the world.