The aim of this study was to determine if a periodontal ligament can form around self-tapping, screw type titanium dental implants. Implants were inserted in contact with the periodontal ligament of root tips retained in the mandibular jaws of 7 monkeys. In each side of the mandible, 1 premolar and 2 molars were removed in such a manner that in approximately half the cases, the root tips were retained. Following healing, the experimental areas were examined on radiographs, and sites were selected for the insertion of the implants, so that every second implant would have a close contact to the retained root tips. Three months after placement of the implants, the animals were sacrificed, and ground sections were produced for histological analysis. The results demonstrated that newly-formed cementum had become deposited on the implant surface in the contact area between the implant and the retained roots, whereas osseointegration was consistently found on the remaining part of the implant surface as well as on the entire surface of the implants placed without contact to the retained root tips. The study has shown that, when placed in contact with periodontal ligament tissue of retained roots, a periodontal ligament can form on self-tapping, screw type titanium dental implants in areas where a void is present between the surrounding bone and the implant at the time of insertion.