Good written communication skills are essential to the practice of medicine and avoidance of medical error. The hospital discharge letter is probably the most important of all written communications between hospital and General Practitioner. However, discharge letters vary greatly in quality, structure, cohesion, and readability. Most discharge letters are written by junior doctors and frequently omit important information. The School of Medicine at University College Cork developed a comprehensive check-list i-phone application to improve the quality of hospital discharge letters. The CLAS scale lists the key elements of a discharge letter - reason for admission, investigations, results, diagnosis, problem list, medications, management plan, name and contact details of doctor writing the letter etc. There are 4 pages of items, divided into various sections. Either a section heading or an individual item can be ticked. Most items score 1, but some items of particular importance, such as medication, score higher. Total CLAS score is 50. At the end, the user is shown his total score and can swipe to see a list of unchecked items. By using the CLAS application as a point-of-practice reference tool, doctors and medical students can improve their letter-writing skills, decrease the risk of medical error and improve patient safety.