This work attempts to demonstrate the root causes of failure of the bearing of rail vehicle wheel sets. The work presents the recommended methodology for analyzing damage to the bearing of rail vehicle wheel sets. It was important that the end result of the analyzes was to correctly identify the root cause of the bearing failure. The results of the failure analysis of selected bearings showed that the most probable causes of their failure were: irregularities during the maintenance phase (including failure to comply with inspection intervals), lack of sufficient supervision and/or failure to properly secure the bearing pressure cap mounting bolts, intrusion of external contaminants and/or contamination of the lubricant at the stage of installation and maintenance activities, electrical erosion. The above-mentioned possible causes of bearing damage provide important information that allows for better prevention of damage.