We investigated clinical data, sweat electrolytes and cystic fibrosis (CF) mutations in twelve patients with congenital bilateral aplasia of vasa deferentia (CBAVD) to debate arguments for diagnosing CF. Sweat chloride concentration was definitely raised in four patients. Three patients are CF compound heterozygotes. Six patients are CF heterozygotes. This result reinforces the hypothesis that white males with CBAVD might have a mild form of CE.