BACKGROUND: Obese individuals have been reported to have a heightened desire for and ability to identify sweets when compared with leaner persons. Smell, like taste, may also be altered in obese persons compared with leaner subjects. This study was designed to determine if the sense of smell is different between morbidly obese and moderately obese individuals. METHODS: 101 adult volunteers undergoing preoperative evaluation completed the 12-item Cross-Cultural Smell Identification Test (CC-SIT) before surgical intervention. Age, BMI, and smoking history were also obtained. RESULTS: 101 subjects completed the preoperative CC-SIT (87 female, 14 male). Mean age of the subjects was 40 +/- 12 years. Mean BMI was 42.5 +/- 12.5 kg/m(2). 46 subjects (46%) had a BMI >45. 21 were smokers (21%). 9 subjects (9%), all female non-smokers, had a CC-SIT score representing olfactory dysfunction. Subjects with BMI >45 were more likely to have olfactory dysfunction than subjects with BMI <45 (16% vs 4%, P <0.05). CONCLUSION: Morbidly obese individuals are more likely than moderately obese individuals to demonstrate CC-SIT scores consistent with olfactory dysfunction. The reason for this is unclear but is probably related to metabolic changes occurring in morbidly obese individuals.