Background: Cystic Fibrosis (CF) is a life-threatening recessive genetic disorder resulting from mutations in the gene encoding the fibrosis transmembrane conductance regulator protein (CFTR). The CF clinical phenotype shows wide variation ranging from severe disease in early childhood in those homozygous for the p.Phe508del mutation to absence of the vas deferens in otherwise healthy men homozygous for the p.Arg117His mutation. Materials and Methods: DNA was extracted from whole blood from 62 patients with CF. The CFTR mutation was determined by Allele-Specific PCR assay. The spearman and linear regression analysis were used to obtain the correlation between phenotype and genotype relationship. Results: Out of total 62 patients, 35 (56.4%) were male. The mean age of the patients was 15.56 ± 6.65 years. Mutations in CFTR were detected in 64.5% of the patients. The commonest mutations were p.Phe508del (33.9%), p.Arg117His; [5T] (5.64%), p.Arg117His; [7T] (4.03%) and p.Trp1282X (5.64%). Mutations p.Ile507del (4%), p.Gly542X (4%), p.Asn1303Lys (2.42%), c.489+1G>T (1.6%), p.Gly551Asp (1.6%) and c.1585-1G>A (1.6%) were also detected. Most mutations were detected in west and south of Iran, while p.Phe508del mutation was dominant mutation (75%) in east and southeast of Iran. The study showed either an association between this mutation with severity of disease and sex or an association between p.Arg117His mutations and age at diagnosis. Conclusion: The geographic distribution of gene mutation in Iranian cystic fibrosis patients was very heterogenic. In spite of the study that showed a correlation between p.Phe508del and severity of disease, to find any correlation between genotype and phenotype a broad and multi-centered study is recommended.