BACKGROUND In free fibular flap surgery, the graft's low vertical height and tendency to resorb over time have been considered potential drawbacks. This study investigated (1) short- and long-term bone resorption in free fibular grafts; (2) resorption behavior of fibular grafts versus dentulous and edentulous autochthonous mandibular bone; and (3) factors that potentially influence long-term bone atrophy, such as site of reconstruction, presence of osseointegrated dental implants, patient age, and adjuvant radiation therapy. METHODS Between 1992 and 2004, 113 patients received free fibular grafts. Fifty-four of these patients were examined retrospectively. Postoperative Panorex examinations assessed loss of bone height per month. Standardized miniplate measurements served as a reference to prevent errors caused by projection on magnification. RESULTS Follow-up ranged from 6 months to 12 years. According to Jewer's classification, the following defect types were found: L, 23 (42.6 percent); H, five (9.3 percent); C, two (3.7 percent); LC, 12 (22.2 percent); HC, nine (16.7 percent); and LCL, three (5.6 percent). Radiographic analysis revealed a monthly atrophy of 0.04 +/- 0.08 mm (mean +/- SD) for fibular bone, 0.14 +/- 0.11 mm for dentulous mandibula, and 0.20 +/- 0.17 mm for edentulous mandibula. The difference in bone loss between fibula and edentulous or dentulous bone was significant (Friedman's test and Wilcoxon paired-sample test, p < 0.0001 and p = 0.02, respectively). Investigated factors had no significant influence on bone resorption rate. CONCLUSIONS Fibular grafts show short- and long-term stability. Their rate of atrophy is significantly lower than that of edentulous or dentulous mandibular bone. Thus, implants can be inserted into this bone graft just as successfully as they are inserted into adjacent mandibular bone when the same bone height is present.