Morbidly obese individuals have altered sense of taste and smell. Gastric bypass (GBP) alters taste but olfactory function has not been evaluated. Changes in these senses may influence dietary preferences following GBP. Our aim was to evaluate the effect of abdominal operation, specifically GBP, and weight loss on olfactory function. Fifty-five persons undergoing GBP and cholecystectomy and 40 persons undergoing cholecystectomy (CC) alone were administered the Cross Cultural Smell Identification Test (CC-SIT) preoperatively and 2 and 6 weeks postoperatively. Patients undergoing GBP underwent further tests at 3, 6, 9, and 12 months. Body mass index (BMI) was also assessed. Mean BMI was significantly greater preoperatively in the GBP group (50.6 ± 8.0 vs. 30.6 ± 7.3 kg/m(2), p < 0.05). Significantly more GBP patients had abnormal CC-SIT results preoperatively (12.7% vs. 5.0%). There were no significant differences in percentage of abnormal tests at 2 and 6 weeks within groups but remained lower in CC patients (2 weeks, GBP 6.2% vs. CC 5.7%; 6 weeks, GBP 9.8% vs. CC 3.2%, p < .05). BMI decreased in the GBP group at 12 months (50.6 ± 8.0 preoperatively to 31.9 ± 6.9 p < 0.05). Absolute olfactory dysfunction (AOD) was present at each interval up to 12 months after GBP. Only 22% of patients with AOD remained obese. GBP does not appear to influence olfactory function. AOD present in morbidly obese persons is not affected by weight loss. These findings support that olfactory dysfunction may be a contributing factor to the development of obesity.