We report a clinical case of horizontal root fracture in the mandibular first premolar induced by a traffic accident. The fractured tooth spontaneously healed and diagnosed radiographically after 2 years. Fractured fragments were separated by a narrow radiolucent line and the edges were rounded, and healing of the tooth is likely to be related to interproximal connective tissue healing. Our case is an example of spontaneously healed fracture roots. An interesting finding is that the healing was observed even in the presence of two root canals, the vitality of the pulp was preserved and displacement of fragments were prevented.