Pneumatization of the maxillary sinus limits the quantity of alveolar bone available for implant placement and may result in a lack of primary stability and difficulty in achieving osseointegration. The purpose of this study was to retrospectively analyze a group of patients who had implants placed in the posterior maxilla, calculate the prevalence of sinus augmentation, and identify factors related to sinus augmentation. With institutional review board approval, dental records from a population of patients who had implants placed in the maxillary posterior region between January 2000 and December 2004 were used to create a database. Independent variables were classified as continuous (age of the patient at stage 1 implant surgery [S1], time between extraction and S1, time between extraction and sinus augmentation, and time between sinus augmentation and S1) and categorical (gender, implant failure, American Society of Anesthesiologists system classification, smoking, osteoporosis, residual crestal bone height, implant position, implant proximity, prostheses type, and implant diameter and length). The dependent variable was the incidence of a sinus augmentation procedure. Simple logistic regression was used to assess the influence of each factor on the presence of sinus augmentation (P < .05). The final database included 502 maxillary posterior implants with an overall survival rate of 93.2% over a mean follow-up period of 35.7 months. Of 502 implants, 272 (54.2%) were associated with a sinus augmentation procedure. Among variables, residual crestal bone height (P < .001), implant position (P < .001), implant proximity (P < .001), prosthesis type (P < .001), implant failure (P < .01), and implant diameter (P < .01), were statistically associated with sinus augmentation. Within the limitations of this retrospective study, the results suggest that more than half (54.2%) of the maxillary posterior implants were involved with a sinus augmentation procedure. The prevalence of sinus augmentation increased with decreased residual crestal bone height, more posterior implant locations, and complete or partial edentulism. Sinus augmentation was significantly associated with implant failure and wide implants.