Intracoronal and intracanal diagnosis (ICD) are important aspects of the endodontic diagnostic process. The intracoronal diagnosis of the pulp cavity is completed before embarking on the root canal treatment itself, while the intracanal diagnosis of the root canal systems continues throughout the instrumentation of the root canal. During this diagnostic process, the endodontist records and documents the findings using optical magnification and coaxial light. The ICD serves to verify the preliminary diagnosis and facilitates the early detection of potential complications as well as an early identification of non-salvageable teeth. Therefore, this diagnostic step is recommended both before and during root canal treatment. Keywords: dental operating microscope, diagnostics, endodontic access cavity, loupe, prognosis