Rationale:Most maxillary lateral incisors have only 1 root and 1 root canal; the presence of both double roots and double canals is extremely rare and can lead to persistent symptoms if not properly diagnosed.Patient concerns:A 36-year-old female presented with a 3-month history of discomfort in the upper left anterior tooth, following prior root canal treatment performed 2 years earlier for pulp necrosis.Diagnoses:Cone beam computed tomography imaging revealed a left maxillary lateral incisor (tooth 22) with double roots and double root canals, with chronic apical periodontitis associated with the untreated palatal canal.Interventions:The patient underwent root canal retreatment involving the removal of old filling material, negotiation and preparation of the missed palatal canal using manual and rotary files, calcium hydroxide dressing, and final obturation with cold lateral compaction and gutta-percha.Outcomes:The patient's symptoms resolved completely after retreatment, and no discomfort was reported during a 1-year follow-up.Lessons:Dental practitioners should possess a comprehensive understanding of the typical anatomy of the dental root canal system and remain cognizant of the potential variations in root canal configurations. When root canal variation is suspected, meticulous examination of the pulp chamber floor, altering the X-ray projection angle, or conducting a high-resolution cone beam computed tomography scan is essential to ensure accurate diagnosis and prevent missed canals, ultimately improving treatment success.