The incidence of cystic fibrosis related diabetes (CFRD) has risen significantly as patients' survival improves. Early diagnosis of CFRD is crucial to prevent the unnecessary deterioration of lung function and nutritional status, both of which affect the patient's overall survival. The oral glucose tolerance test (OGGT) is the accepted method for detecting CFRD. The Cystic Fibrosis Trust guidelines (2004) recommend that patients with CF over the age of twelve years should be screened annually. Most hospitals use an annual OGTT. Performing OGTT on all CF patients is inconvenient and may not be cost effective, as patients have to starve overnight and need to spend an extra 2 hours in the hospital in addition to all the other annual review tests. In our centre, a selective approach is used. If patients have an abnormal random blood glucose and /or abnormal glycosylated haemoglobin (HbA1c) and/or symptoms of hyperglycaemia or unexplained weight loss then an OGTT will be performed.