The reasons for mistakes in the interpretation of neuro-imaging examinations are similar to those in radiology in general, i.e. poor technique, artefacts, failure in perception, lack of knowledge and misjudgment. The reader may commit so-called scanning errors (overlook the primary or additional lesion), recognition errors or decision-making errors. Factors like misleading-or even correct clinical history, presence or absence of previous studies, knowledge and experience of the reader, etc, may lie behind an incorrect interpretation. Although experience increases the accuracy, marked differences have been reported between the most experienced readers. In neuro-imaging there is an increased risk of errors due to the large (and increasing) number of images to be reviewed per case, the complexity of some of the images and of the analysis. The risk of errors is increased also due to artefacts, especially in the interpretation of MRI, or due to poor imaging quality, for example in MRA or CTA. In the present lecture different causes for mistakes, such as artefacts, misdiagnosis due to lack of-or comparison to wrong previous studies, poor imaging technique and wrong clinical information will be addressed. Learning Objectives: