Congenital absence of the vas occurs in up to 1% of men. Congenital unilateral absence of the vas deferens can be related to cystic fibrosis transmembrane conductance regulator mutations or in 79% of cases, renal agenesis. We present a case of each, diagnosed in children at operation for elective inguinal hernia repairs. One patient had associated ipsilateral renal agenesis with a normal cystic fibrosis screen. The other patient had an ipsilateral pelvic kidney and a mutation detected on cystic fibrosis screening. Current understanding of the embryology of the relationship between these defects would seem to be supported by our cases.