Epididymal stones have been reported in roosters in the USA and Japan. The cause of this dysfunction, which is associated with low fertility, is not known. The hypothesis of the present study is that a potential cause is the aggressive selection of birds over many centuries based upon female egg laying traits, without concern for potential effects on the male. If this hypothesis is correct, one potential consequence would be the presence of epididymal stones only in domesticated fowl and this observation would be worldwide in distribution. The present study investigated epididymal lithiasis in Brazilian crossbreed roosters and two other fowl strains, in addition to several domestic and wild bird species. The efferent ductules contained stones in 94.3% of the roosters, but stones were absent in all other domestic and wild birds. The stones were irregular in shape, size and colour and consisted mainly of calcium. In affected roosters, the efferent ductules showed epithelial cell vacuolization and sloughing and peritubular mononuclear cell infiltration, culminating with atrophy. Signs of epithelial re-canalization were seen in ductules occluded by abnormal content, such as stones. In the testis, decrease in mass, sloughing of epithelium, mononuclear cell infiltration and tubular atrophy occurred. No correlation was found between the occurrence of stones and a positive test for ELISA IBV (infectious bronchitis virus), or between the number of stones and calcium concentration in water and food, indicating that IBV infection and calcium in the diet were not related to stones formation. This study confirms and extends information about the epididymal lithiasis, which appears to be unique for roosters but to occur around the world. The severity of the lesion points to potentially severe economical impact in the poultry industry.