Cystic fibrosis, presenting in childhood, is a hereditary disease that proceeds with the dysfunction of all exocrine glands. Two months infant who was born premature admitted with respiratory distress. The infant's oxygen saturation was 80% and white sphere was 23.000/mm3. Clor levels were found as 88 mEq/l and 103 mEq/l by sweat chloride test. Cystic fibrosis was diagnosed. The patient not responded to treatment and was positive CMV-DNA was detected. The patient responded well to ganciclovir treatment. When a case with cystic fibrosis does not respond to treatment, another underlying causes should be considered.