Cystic fibrosis is an autosomal recessive disease caused by a wide spectrum of mutations in the gene encoding for the cystic fibrosis transmembrane conductance regulator protein. These mutations that correlate with different phenotypes, vary in their frequency and distribution in different populations. In this study missense mutation R117H that associated with the different clinical symptoms was analyzed in CF patients. Fifty five non relative Iranian cystic fibrosis patients aged between four month to eighteen years old living in the north of Iran, Mazandaran province were screened for clinical presentation and also for R117H mutation by reverse dot blot method. the most clinical presentation was pulmonary disorder and non of the patients had R117H mutation these finding will be use in genotypes and phenotypes correlation and planning genetic counseling.