Congenital bilateral absence of the vas deferens (CBAVD) was once thought to be a distinct clinical entity, but genetic similarities in men with cystic fibrosis (CF) and CBAVD are described increasingly. We evaluated the clinical status, growth and nutritional state, and respiratory function of 18 men with CBAVD to determine whether these men with different CF transmembrane regulator (CFTR) genotypes may have clinical evidence of mild CF. Following a thorough history and examination, pulmonary function tests, sweat test, and renal ultrasound were performed. Genetic evaluation for 50 known CF mutations, screening for private mutations (single-strand conformational polymorphism and direct sequencing), and assay of the length of the polypyrimidine tract in the splice site acceptor of intron 8 was performed. A history of pulmonary disease was present in three, and an additional man had some features suggestive of malabsorption. Results of general physical examination and anthropomorphic measurements were unremarkable in all patients, with a mean (SD) body mass index of 26 (3). Pulmonary function tests of large and small airway function as well as lung volumes were normal in all except one whose results were consistent with moderate asthma. Five men were compound heterozygotes for CFTR mutations, four of whom had positive sweat tests (sweat chloride > 60 mEq/L). Twelve men were heterozygotes for CFTR mutations while no mutations were identified in one man. Although putative etiologic factors may suggest that men with CBAVD and CFTR mutations could be considered within the spectrum of clinical CF, the authors suggest that in men with CBAVD without any other clinical features of CF, the diagnosis of CF may not be made.