Cystic fibrosis (CF) is the most common autosomal recessive disorder among Caucasians. Early diagnosis and advances in the care of patients with CF have improved survival. Limited data is available regarding its prevalence in high risk Egyptians. It was generally believed that CF is rare among Arabs ; however, the few studies available are suspecting the presence of many undiagnosed patients. The aim of the present study is to determine the prevalence of CF in high risk Egyptian patients referred to the allergy and pulmonology unit through a period of one year. Since the sweat chloride test remains the gold standard for the diagnosis of CF, we used it in the diagnosis of our cases using the standardized methods which is approved by the NCCLS (National Committee for Clinical Laboratory Standards) and the CFF (cystic fibrosis foundation) guidelines which are pilocarpine iontophoresis for induction of sweat and macroduct collector for sweat collection. Analysis of the samples was done by the conductivity analyzer and by the chloridometer. Gene analysis of the positive cases was performed using gene amplification by PCR followed DNA sequencing for detection of delta F508 mutation. Results of the present study showed that the prevalence of CF in high risk patients is 30%, which is more than expected for our population from previous studies. Delta F508 represents 53.3% of the CF patients. The accuracy of the conductivity analyzer was assessed by sensitivity and specificity which are 46% and 100% respectively. By correlation of the severity of the diseases with the sweat test values, it was statistically insignificant. In conclusion, further studies are required for accurate assessment of the CF prevalence and the identification of different mutations in the Egyptian population.