Maxillary sinus membrane elevation and bone graft have been performed routinely in alveolar bone with insufficient residual bone height. There are a number of causes for development of maxillary sinusitis after these procedures. When maxillary sinusitis is caused by sinus membrane elevation, bone graft, and implant placement, various treatment such as medication, incision and drainage (I&D), implant removal, and the Caldwell-Luc procedure can be considered. Removal of an implant or the Caldwell-Luc procedure can be harmful if inflammation is not present in the oral cavity and survival of grafted bone and implant osseointegration can be expected despite the presence of maxillary sinusitis. In this case, functional endoscopic sinus surgery, which was often used in the otorhinolaryngology department, was performed without removal of the implant for a patient with maxillary sinusitis after one month following implant placement. Thus, we report on this case with a review of the literature.