IMPORTANCE The clinical and financial implications of the timing of dental rehabilitation after a fibula free tissue transfer (FFTT) for osteoradionecrosis (ORN) and osteonecrosis (ON) of the mandible have yet to be established. OBJECTIVE To compare the outcomes of primary implantation vs secondary implantation after FFTT for ORN and ON of the mandible. DESIGN, SETTING, AND PARTICIPANTS A retrospective review was conducted of 23 patients at a single tertiary academic referral center undergoing primary implantation or secondary implantation after FFTT for ORN and ON from January 1, 2006, to November 10, 2015. INTERVENTIONS All patients underwent FFTT with primary implantation (n = 12) or secondary implantation (n = 11). MAIN OUTCOMES AND MEASURES Outcomes of FFTT, dental implantation, implant use, diet, speech, and disease-free survival were reviewed. Fixed unit costs were estimated based on the mean cost analysis. RESULTS Twenty-three patients (7 women and 16 men; mean [SD] age, 62.4 [8.2] years [range, 24-81 years]) met the inclusion criteria. Of these, 18 had ORN and 5 had ON. Dental implantation was performed at the time of FFTT for 12 patients and was performed secondarily for 11 patients. There were a mean of 5.2 implants per patient performed, for a total of 121 implants. There was 1 complete flap failure in the primary implantation group. Neither flap nor implant complications were affected by the timing of the implantation. Overall, the implant survival rate was 95% (55 of 58) in the primary implantation group and 98% (62 of 63) in the secondary implantation group. Time from FFTT to abutment placement (primary implantation, 19.6 weeks; secondary implantation, 61.0 weeks) was significantly shorter after primary implantation (P < .001). There was no clinical difference in postoperative complications and implant outcomes for ORN vs ON. Improvement in speech and oral competence in the primary implantation group vs the secondary implantation group was not statistically significant, given an experiment-adjusted P = .001 set as significant (normal speech, 9 vs 3; P = .02; and normal oral competence, 9 vs 3; P = .02). Disease-free survival was 91% (20 of 22 patients) overall. Fixed unit (U) costs were 1.0 U for primary implantation and 1.24 U for secondary implantation. CONCLUSIONS AND RELEVANCE Patients undergoing primary implantation after FFTT for ORN and ON had a similar rate of complications compared with those undergoing secondary implantation. However, primary implantation allowed a faster return than secondary implantation to oral nutrition and prosthesis use. The fixed unit cost was reduced for those undergoing primary implantation. Although dental implantation was safe and effective in both groups, the decreased time to use and the decreased overall cost should prompt surgeons to consider primary implantation after FFTT for ORN and ON.