The Hamilton and Zuk model predicts that genes for resistance to various pathogens may be continuously heritable due to selection disequilibria caused by coadaptional cycles of hosts and pathogens. The model further suggests that the expression of male secondary ornaments is condition-dependent and that only individuals with superior genetic disease resistance and vigour can fully express exaggerated secondary ornaments. Female choice is therefore expected to discriminate among males on the basis of secondary sexual characters in order to pass on genes for disease resistance that improve fitness in the offspring. In wild ring-necked pheasants, Phasianus colchzcus, of the Revinge area in southern Sweden, females prefer to mate with long-spurred males and data on reproductive success indicate that they may improve their chicks* survival rate by doing so. Male spur length is positively correlated with age, body size and viability. MHC genotyping for both class I and class II B of pheasant males trapped in the study area identified eight MHC haplotypes and a total of 17 different MHC genotypes. Multivariate analyses revealed that MHC genotype is significantly associated with variation in both male spur length and male viability. These data indicate that polymorphic genes with a central role in immune recognition can be associated with viability and the expression of a condition-dependent intersexually selected male trait, thus supporting essential parts of the Hamilton and Zuk model.