This report describes a case in which failure of conventional root canal therapy presented 17 years following initial treatment. The apical pathology was curetted, the tooth root resected and a root-end filling placed. The possible reasons for failure of the initial orthograde root canal therapy are discussed with the conclusion that the cause may not have been addressed fully by surgical intervention. The case highlights the challenge facing clinicians when assessing failed root fillings, not only in determining the exact cause of failure but deciding the appropriate treatment for the individual tooth and patient.