A case report of an unusual root resorption reaction associated with a graft of hydroxyapatite particles is presented. The hydroxyapatite particles were grafted to treat vertical infrabony defects at the distal aspect of the maxillary left canine and on the mesial side of the mandibular right first molar. The graft sites were monitored at maintenance visits. Root resorption was observed radiographically 9 to 10 months after grafting. The lesions were restored with a light-cured glass-ionomor cement and/or a resin composite. Possible etiologic factors associated with this condition are discussed.