I estimate the frequencies of interracial kin relations, an important indicator of the isolation of racial groups in the United States. I use two techniques to estimate the size and heterogeneity of extended families. First, I develop a simple model that takes account only of kinship network sizes and intermarriage levels by race. This model allows a crude estimation of the frequency of multiracial kinship networks. Second, I produce more precise empirical estimates using a new hot-deck imputation method for synthesizing kinship networks from household-level survey data (the June 1990 Current Population Survey and the 1994 General Social Survey). One in seven whites, one in three blacks, four in five Asians, and more than 19 in 20 American Indians are closely related to someone of a different racial group. Despite an intermarriage rate of about 1%, about 20% of Americans count someone from a different racial group among their kin.