Sinus floor augmentation (SFA) is one of the techniques that has been proposed for improving the long-term retention of dental implants. The procedure involves the creation of a submucoperiosteal pocket in the floor of the maxillary sinus for placement of a graft consisting of autogenous, allogenic, or alloplastic material. Complications of the SFA predominantly consist of disturbed wound healing, hematoma, sequestration of bone, and transient maxillary sinusitis. In this report, we presented an acute maxillary sinusitis complication following internal sinus lifting in a patient with chronic maxillary sinusitis.