Cystic Fibrosis (CF) is a lethal autosomal recessive condition due to a defect at the level of the transmembrane conductance regulator gene which plays a role in cell homeostasis. Numerous mutations have been identified as the cause of this gene defect, with delF508 being one of the most common mutations in Tunisia. This is a case report describing, up to our knowledge, the second case of a patient with CF carrying a rare mutation: W19X. W19X is a nonsense mutation that has been previously identified in only one other Tunisian patient with CF. Since both incidence of this mutation have been described in Tunisia, it seems as if W19X is specific to Tunisian CF patient with significant morbidities. The information provided by this study contributes to defining the molecular spectrum of CF in Tunisia, in the aim of improving genetic testing and prenatal diagnosis.