Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the CF trans-membrane conductance regulator (CFTR) protein. CF is the most common inherited disease of Caucasians, with a carrier frequency of 1 in 25-30 individuals. Even with the impressive advances achieved in the understanding of the molecular basis and physiopathology of CF, it remains a life-threatening disorder that causes severe lung damage and nutritional deficiencies. It is generally accepted that early therapy could delay the progression of lung disease. A number of non-invasive methods are available to monitor disease activity in CF patients; however none of the currently used tools are able to monitor real-time events. Recently high resolution computed tomography (HRCT) has been used to monitor changes in lung structure. However, HRCT does not allow differentiating between acute and chronic lesions. Positron emission tomography (PET) with 18fluoro-deoxy-glucose (FDG) has already been used in a variety of settings to visualize inflammation or infection. FDG-PET imaging appears to be a promising new tool to quantify inflammation as it can detect clinically relevant changes even when no changes or minimal ones are detected by morphologic imaging. PET/CT may consequently be used to evaluate the severity of lung inflammation/infection in CF patients, and therefore the aim of this study is to evaluate the use of PET/CT for the assessment of the severity of lung inflammation/ infection in CF patients.