Congenital bilateral absence of vas deferens occurs in men when the tubes that carry sperm from the testes (the vas deferens) fail to develop normally. This condition can occur alone or as a sign of cystic fibrosis (an inherited disease of the mucus glands). Men with congenital bilateral absence of vas deferens are infertile (unable to conceive a child). The testes usually develop and function normally and the men have normal sexual performance, but sperm cannot be transported through the male reproductive system. When this condition occurs in the absence of typical cystic fibrosis, most men have no other health problems. Some men with the disorder have mild respiratory or digestive symptoms, however.