As part of a collaboration between the Biomedical Primate Research Centre (BPRC) in the Netherlands and the New England Primate Research Center (NEPRC) in the United States, we analyzed DNA sequences of MHC class I (<i>Macaca mulatta, Mamu-A1</i>) and class II (<i>Mamu-DRB</i>) alleles from rhesus macaques with endometriosis and compared the allele frequencies with those of age-matched healthy macaques. This evidence concerns the gene HLA-C and endometriosis.