Data on inbreeding in several contemporary human populations are compared, showing the highest local rates of inbreeding to be in Brazil, Japan, India, and Israel. American populations are noteworthy for their extremely low inbreeding rates, with the mean frequency of first cousin marriages in the United States probably lower than 0.1 per cent. Some localities in Puerto Rico and Sweden show inbreeding levels half‐way between the extremes found in Brazil and Japan and in the United States. For European countries, Denmark, France, Italy, and North Ireland have a mean frequency of first cousin marriages of less than 1 per cent, while England, Wales, Germany, and Holland have a frequency probably lower than 0.5 per cent. The frequency of first cousin marriages in Portugal may lie between 1 and 2 per cent.