Objective: To clarify the mode of root fracture in 32 endodontically treated teeth that resulted in vertical root fracture (VRF) despite the provision of a crown for fracture prevention. Method and Materials: The teeth included in the study underwent root canal treatment and were restored with crowns without the use of an intracanal post. All teeth underwent photo documentation. Clinical signs and symptoms as well as the patients' ages were recorded. The diameters of the roots and the root canal fillings were measured on radiographs. Fractured roots were investigated using a scanning electron microscope (SEM). Results: The mean patient age was 60.2 years. The VRFs in the group occurred most frequently in the mesial roots of the mandibular first molars. The fracture was predominantly buccolingual. The mean ratio measured between the diameters of the root canal obturations and the outer root surfaces in the radiographs was 33.2%. SEM evaluation showed that most fractures ran from the inner to the outer root surface, and the cracks predominantly ran apical to coronal. Conclusion: Endodontically treated and crowned teeth without root canal posts can develop VRFs. The cracks start at the root canal wall in the apical part of the root and extend toward the outer root surface and coronally. Further investigation is necessary to determine the possible causes and evidence of fracture development. Schlagwörter: apical preparation, apical sclerosis, crack development, root canal treatment, vertical root fracture