We conducted a seroepidemiologic study of cytomegalovirus (CMV) infection among 9,928 Inuit (Eskimo), Dene (Indian) and non-native inhabitants of the Northwest Territories (NWT) of Canada between April 1983 and March 1985.4,184 inhabitants of Edmonton, a large predominantly white urban center served as controls. Sera were screened for antibody to CMV by enzyme-linked immunosorbent assay (ELISA). The prevalence rates of CMV antibody increased with age in all ethnic groups. By the age of two years 69.2 percent of Dene, 63.5 percent of Inuit, 33.3 percent of non-native and 22.9 percent of Edmonton children had CMV antibody. Over the age of five years Inuit children had higher rates of CMV antibody than Dene children (P < .05) reflecting differences in infant adoption, breastfeeding practices and patterns of child care in the two native groups. By the age of 15 to 19 years 8 1. I percent of Dene and 88.5 percent of Inuit women had CMV antibody compared to 48.8 percent of non-native and 50.9 percent of Edmonton women (P < .05). Native children had higher prevalence rates than non-native children living in the NWT (P < .05). Compared to similarly aged Edmonton residents, non-native children in the NWT 2 to 4 years and 5 to 9 years of age had a higher prevalence of CMV antibody (P < .05). We observed a higher prevalence rate of CMV antibody among non-native children (1&14 years) and young women (1 5-1 9 years) living in predominantly native communities compared to those living in predominantly non-native communities in the NWT (P < .05). The seroprevalence in 60 non-native female health care workers in the NWT was not significantly different from that seen in comparably aged Edmonton women.