Upper and lower gastrointestinal endoscopy examinations are performed daily as routine diagnostic procedures in a large number of patients with nonspecific indications, such as heartburn, pain, anaemia, bleeding, workup of portal hypertension and so on. Most of the examinations will point to a classic diagnosis (e.g. peptic disease, cancer, variceal management), but sometimes we see patients who've had multiple diagnostic endoscopic procedures in the previous few months with nonconclusive findings. The diagnostic mistakes discussed here are those that sprang to mind based on our endoscopic experience and they are discussed in an evidence-based approach. For therapeutic endoscopic procedures (e.g. ERCP and resections), we present the most important mistakes that are often seen in our practice and have major consequences for the patient. We propose, from our experience, a simple approach to avoid these mistakes.

 Upper GI-endoscopy is one of gastroenterology's most frequently performed diagnostic and interventional methods. Even though gastroscopy is believed to be a routine investigation - which is the greatest mistake of all - several pitfalls in performance can cause serious problems or misdiagnoses. Struggles in accurately describing and classifying abnormal findings can occur and concern the correct basic technique of endoscope introduction, and the correct way of investigating the mucosal surface in total, with several available imaging modalities such as virtual chromoendoscopy or magnification. Which classification systems should be used? The decision to perform additional workup needs to be made immediately during the ongoing endoscopy. Is it necessary to take biopsies, or should it even be avoided due to potential interference with a later endoscopic resection? This article answers the questions, highlights the most common mistakes with clinical relevance and expands on how to avoid them.

Colonoscopy is a complex procedure requiring both technical and non-technical skills. Performing colonoscopy also requires manual and visuospatial skills, interpretation of pathology, patient communication and a wide range of advanced therapeutic technologies. The clinical intention of colonoscopy must be individualised, and diagnostic and/or therapeutic intent rationalised, given the procedures invasive nature and associated risks. Furthermore, each colonoscopy differs due to patient factors, sedation strategy, anatomical configuration, technical challenges and endoscopist skills. Endoscopists must, therefore, demonstrate a wide range of expertise whilst working effectively in a team to manage the patient safely. It is not, therefore, surprising that mistakes in colonoscopy can occur. This article focuses on six common mistakes in colonoscopy that can be avoided to improve the procedure's safety and deliver a high-quality procedure. This, in turn, can reduce the rates of post-colonoscopy colorectal cancer (PCCRC) and improve patient experience and adherence to colonoscopy surveillance programmes. This article is based on evidence in conjunction with our collective clinical and research experience of errors in endoscopy and patient safety.