This evaluation correlates maxillary sinus 3D morphology with bone regeneration. In 39 patients with crestal bone ≤ 2 mm, mineralized human bone allografts were used to augment the sinus floor through the crestal window sinus elevation approach. CBCT was used to measure the buccopalatal diameter (BPD), mesiodistal diameter (MDD), and hemi-ellipsoidal volume (Vh) in all sinuses. A bone core biopsy sample was taken at implant placement (4 to 5 months after sinus augmentation). Microradiographs of methacrylate-embedded sections were used to evaluate the amounts of bone, residual graft, and soft tissue. All 51 implants placed in the 39 patients successfully osseointegrated. A linear regression analysis showed that as BPD, MMD, and Vh increased, the amount of bone gain decreased and the amount of soft tissue increased (P < .05). The amount of residual graft was little affected by sinus morphology. Microradiographic data were grouped into four different sinus types (from small to great) using BPD and Vh medians. The best amount of bone formation was achieved in the narrow and short sinus type, while no great differences were found in the remaining three sinus types. Understanding of 3D sinus cavity morphology, especially the buccopalatal diameter and mesiodistal dimensions, is fundamental for achieving the best possible sinus augmentation outcomes.