Findings in 200 cases of root resection of first maxillary molars showed perforation to the sinus in half of the cases. In 42% of the cases, the first maxillary molar had root resection performed in a subacute or acute state of infection. Only two cases developed postoperative sinusitis. Antibiotic treatment was indicated preoperatively in 3% and postoperatively in 5%. Postoperative symptoms, such as pain and swelling, were usually moderate, possibly because of a nontraumatizing operation technique, a careful removal of infected tissue, and a good drainage by loose suturing.