Sixteen patients with clinical features of postoperative gastritis who had been advised to have a Roux-en-Y diversion were studied prospectively. Studies were done pre- and postoperatively (mean follow-up, 4.9 years; range, 3.8 to 6.9), and the findings were compared with those in 11 control subjects with previous enterogastric anastomosis but with no symptoms. The patients had higher concentrations of bile acids and trypsin in gastric samples than did controls. Patients had greater endoscopic changes, although mucosal histologic characteristics were similar in both groups. Administration of aluminum hydroxide or cholestyramine reduced the aqueous concentrations of bile acids in gastric contents. Roux-en-Y diversion virtually eliminated duodenogastric reflux, and gastroscopic appearances returned to normal. However, Roux-en-Y diversion did not change mucosal histologic characteristics. Symptom scores were reduced in the early postoperative period, but bilious vomiting was the only symptom alleviated consistently and permanently. As a treatment for postoperative gastritis, Roux-en-Y diversion offers potential but limited benefits.