Purpose: The aim of this study was to evaluate the influence that lateral window dimensions may have on maxillary sinus augmentation outcomes. Materials and Methods: Patients requiring maxillary sinus augmentation by a lateral window approach and delayed implant placement were recruited in this study. Approximate window dimensions (AWD) were calculated in mm2 at the time of the surgical intervention. In all cases, a mixture of cortical and cancellous allograft particles was used as the sole grafting material. Patients were followed for 6 months. At the time of implant placement, bone core biopsies were harvested. Transversal circular samples were histomorphometrically analyzed. Proportions of vital bone (VB), remaining allograft particles (RA), and nonmineralized tissue (NMT) were quantified. Analysis of correlation of AWD with %VB, %RA, and %NMT was performed using a statistical model. Results: A total of 24 maxillary sinus augmentation procedures were performed in 21 patients. One patient developed an infection after grafting and was excluded. Histomorphometric analysis showed that mean %VB was 21.69% ± 16.30%, %RA was 23.51% ± 16.33%, and %NMT was 55.08% ± 8.52%. A strong negative correlation was observed between AWD and %VB (r = -0.621; P = .0007), a marked positive correlation was found between AWD and %RA (r = 0.565; P = .002), and a minimal positive correlation, without statistical significance, was found between AWD and %NMT (r = 0.076; P = .365). Conclusions: The results of this study suggest that AWD may have an important influence on the maturation and consolidation of a mixture of cortical and cancellous allograft in the maxillary sinus. Keywords: bone grafting, dental implants, maxillary sinus