The International Haplotype Map Project (HapMap) has provided an essential 
database for studies of human population genetics and genome-wide association. 
Phases I and II of the HapMap project generated genotype data across ∼3 million 
SNP loci in 270 individuals representing four populations. Phase III provides 
dense genotype data on ∼1.5 million SNPs, generated by Illumina and Affymetrix 
platforms in a larger set of individuals. Release 3 of phase III of the HapMap 
contains 1397 individuals from 11 populations, including 250 of the original 270 
phase I and phase II individuals and 1147 additional individuals. Although some 
known relationships among the phase III individuals have been described in the 
data release, the genotype data that are currently available provide an 
opportunity to empirically ascertain previously unknown relationships. We 
performed a systematic analysis of genetic relatedness and were able not only to 
confirm the reported relationships, but also to detect numerous additional, 
previously unidentified pairs of close relatives in the HapMap sample. The 
inferred relative pairs make it possible to propose standardized subsets of 
unrelated individuals for use in future studies in which relatedness needs to be 
clearly defined.