OBJECTIVE We aimed to evaluate the performance of hybrid bone single-photon emission computed tomography (SPECT)/computed tomography (CT) in predicting bone graft viability after maxillary or mandibular reconstructive surgery with vascularized bone grafts. METHODS We retrospectively reviewed 46 bone planar scintigraphy and SPECT/CT images of 45 adult patients taken at 1 week (5-8 days) after maxillary or mandibular reconstructive surgery with vascularized bone grafts. By visual analysis, two nuclear medicine physicians scored the uptake degrees of each bone graft segment compared with the calvarium uptake on planar bone scintigraphy and SPECT/CT, respectively (0 = absence of uptake, 1 = less uptake, 2 = similar uptake, and 3 = more uptake). The imaging results were compared with clinical follow-up for assessing bone graft viability. RESULTS During follow-up, five bone graft segments were surgically removed and confirmed as nonviable-one had a score of 0, although the other four had a score of 1-3 on planar bone scintigraphy. All five bone graft segments were scored 0 on SPECT/CT and eventually confirmed as nonviable. All other graft segments with a score of > 1 on SPECT/CT were viable and uneventful. The anatomical CT information on SPECT/CT images was helpful in discriminating bone graft uptake from adjacent bone or soft tissue uptake. CONCLUSIONS The absence of tracer uptake by the vascularized bone graft on bone SPECT/CT at 1 week after maxillary or mandibular reconstructive surgery can predict graft failure. Bone SPECT/CT can be used to predict vascularized bone graft viability postoperatively.