Background: Morbidly obese individuals have been shown to have altered taste and smell. Gastric bypass surgery has previously been shown to alter taste. Gastric bypass surgery may also alter smell and the combination of these changes may account for changes in food tolerance and appetite in morbidly obese persons. The aim of this study was to evaluate the effect of abdominal operation, specifically gastric bypass, on olfactory function. Methods: 55 persons undergoing Roux-en-Y gastric bypass (GBP) and cholecystectomy and 40 persons undergoing cholecystectomy (CC) alone were administered the Cross Cultural Smell Identification Test (CC-SIT) pre-operatively and at 2 and 6 weeks postoperatively. Patients undergoing GBP underwent further tests at 3,9, and 12 months. Body mass index (BMI), age, and gender were also assessed pre-operatively and BMI was followed at the time of post-operative testing. Results: Mean BMI was noted to be significantly greater in the GBP group (50.6 v. 30.6, p<0.05). Age and gender distribution were similar between groups. 12.7% of GBP patients and 5% of CC patients had abnormal CC-SIT results pre-operatively. Post-operatively, there were no significant differences in percentage of abnormal tests at 2 and 6 weeks (2 weeks: GBP 7.5% v CC 5.8%, p>0.05; 6 weeks: GBP 10.8% v CC 3.2%, p>0.05). BMI was noted to decrease in the GBP group from 50.6 pre-operatively to 34.2 at 12 months post-operative with 10.8% olfactory dysfunction. Conclusion: Olfactory dysfunction in morbidly obese persons does not appear to be affected by weight loss. Additionally abdominal operation does not appear to influence olfactory function.