Objective. To evaluate the association between sinus bone graft and the development of fungus ball (FB) of the maxillary sinus. Study Design. The charts of all patients seen for surgical treatment of maxillary sinus FB following sinus bone grafting between 2006 and 2014 were reviewed. The charts of 49 participants were selected from our internal registry for comparison as controls. The association between FB and age, gender, smoking habits, associated co-morbidities, and bone grafting material was evaluated. FB of the maxillary sinus was estimated by using an odds ratio with a Yates' correction. P values were computed using Fisher's exact test, and the statistical significance was set at a P value < .05. Results. All 13 cases (100%) with FB of the maxillary sinus had received anorganic bovine bone as the bone substitute (P ¼ .0001). There were significantly more women in the case group than in the control group (84.6% in the cases vs 40.8% in the controls; P ¼ .01).Conclusions. This study demonstrated a significant association between a specific deproteinized bovine bone substitute use as sinus bone graft material and subsequent development of FB of the maxillary sinus. (Oral Surg Oral Med Oral Pathol Oral Radiol 2016;121:e143-e147) Fungus ball (FB) represents the most common form of noninvasive extramucosal fungal infection involving the paranasal sinuses and is encountered in almost 28.5% of patients suffering from chronic maxillary sinusitis. 1-3 Aspergillus fumigatus is, by far, the most frequent causative agent found in Europe, and the root canal overfilling with the passage of zinc oxide endodontic sealers into the maxillary sinus is the most commonly recognized risk factor for the development of FB in up to 84% of patients. [1][2][3][4][5][6] Although this form of sinusitis typically affects healthy adults and has a striking female predominance, several pathologic conditions, such as diabetes, immunodeficiency diseases, and immunosuppressive and chronic corticosteroid and antibiotic treatments have been pointed out as potential predisposing factors favoring the colonization and subsequent overgrowth of the fungal hyphae. [1][2][3] Since its first report in 1980 by Boyne and James, grafting of the maxillary sinus floor has rapidly become the most common surgical procedure used to increase the subantral alveolar bone height of the posterior maxilla for subsequent dental implant placement. 7 Although reported as a predictable and reliable procedure, sinus bone graft has, nevertheless, been associated with several intra-and postoperative complications, such as sinus membrane perforation, maxillary sinusitis, wound dehiscence with graft exposure, and graft infection. In most cases, complications resolve with no need for further surgery and with no substantial impact on implant survival; however, in some cases, complications may lead to complete loss of the graft material, thus compromising the subsequent implant-supported dental restoration. [8][9][10][11][12][13][14][15][16][17] Although the literature co...