Myxomas are benign mesenchymal tumors of uncertain etiology. They can arise from odontogenic tissue, as well as from the sinonasal tract and from the facial and temporal bones, apparently from nonodontogenic mesenchyme. Although histologically benign, myxomas are locally invasive. Histopathology demonstrates a characteristically hypocellular lesion with loose stellate cells. We describe the case of a 48-year-old woman with a nonodontogenic maxillary sinus myxoma that invaded the sphenoid sinus and pterygopalatine fossa. We removed the mass via a combined endoscopic and gingivobuccal approach. The rarity of a nonodontogenic sinonasal myxoma extending into the sphenoid sinus and pterygopalatine fossa is the basis for our presentation of this case.