The transsphenoidal approach to the pituitary (TSA) is currently the most common approach used to treat pituitary tumors. The surgical technique necessitates an incomplete stripping of sphenoid sinus mucosa. Long-term postoperative magnetic resonance imaging (MRI) evaluation of the sphenoid sinus has not been reported. A retrospective review of patients undergoing a TSA at the University of Washington Hospitals was performed. Preoperative scans were compared with postoperative scans done during three time intervals, Group 1 had scans at 1 to 12 weeks postoperatively; 10 of 10 patients had sinus effusions. Group 2 had scans at 6 to 18 months postoperatively; 22 of 31 had mucosal abnormalities. Group 3 had scans at 2 to 3 years; 7 of 9 were abnormal. MRI evaluation indicates that a majority of patients have both acute and chronic sphenoid sinus abnormalities after TSA.