The objectives of the present study were to test odor identification ability in patients with multiple sclerosis (MS) and to examine possible correlations between smell identification test scores and various clinical variables. We performed a case-control study comparing the Cross Cultural Smell Identification Test scores of 40 patients with definite multiple sclerosis with those obtained in 40 age-, sex- and smoking-habit-matched healthy controls. The neurological impairment, the disability, the cognitive performances and the psychological functioning were also assessed. Patients with multiple sclerosis scored significantly poorer than controls on the Cross-Cultural Smell Identification Test (P<0.001). Olfactory function was borderline normal in four (10%) and abnormal in five (12.5%) MS patients, whereas it was normal in all controls (P<0.02). Significant correlations between the smell identification score and symptoms of anxiety (r=-0.43, P=0.006), depression (r=-0.42, P=0. 008) and severity of neurological impairment (r=-0.32, P=0.05) were found. Only two (5%) patients with multiple sclerosis reported having episodes of smell loss, suggesting a low level of awareness of this problem. Although smell changes are rarely reported, olfactory function is impaired in a considerable number of patients with MS. The observed association between decreased odor identification ability and symptoms of anxiety and depression in our patients suggests that mood and anxiety disorders have to be considered in assessing olfaction in MS patients. Clearly, smell disturbances deserve greater attention from health professionals and caregivers dealing with such patients.