Dens invaginatus (dens in dente) is a common dental anomaly with a reported prevalence of between 0.04% and 10%. It typically affects permanent maxillary lateral incisors, central incisors and premolars. These developmental lesions are less common in mandibular teeth and are extremely rare in canines and molars. This report describes a rare case of dens invaginatus (Oehlers type II) in a permanent mandibular canine. The tooth was mature with a closed apex and showed apical pathosis. The tooth was treated endodontically using a non-surgical technique with hand endodontic files, and then followed up after a period of 8 months. A follow-up radiograph showed some healing of the lesion. © 2010 The Authors. Journal compilation © 2010 Australian Society of Endodontology.