A forty-three-year-old man with diabetes and insulin treatment was referred to endodontic specialist because of a pain in tooth 33. Clinical examination revealed a sinus tract and sensitivity to percussion and palpation. Part of the lingual surface was filled with a temporary filling. A radiograph showed that the tooth was previously root filled. The old root filling had been done one year earlier. The root fillings seemed technically of good quality and correct length. Retreatment for apical periodontitis was started.