AIM: Alzheimer's disease (AD) is one of the most significant diseases associated with ageing. As the disease progresses, symptoms including olfactory dysfunction often appear along with cognitive dysfunction. We examined olfactory and other indexes to investigate correlations between them and the validity of an olfactory test for screening for AD. METHODS: To assess whether odorant identification will be a useful diagnostic tool, we investigated the olfactory ability of Alzheimer's disease patients (ADs) using the Odor Stick Identification Test for the Japanese. As a control, we compared ADs to aged people without AD or dementia. To investigate the relationship between olfactory loss and severity of AD, we used the Mini-Mental State Examination, Alzheimer's Disease Assessment Scale, biomarkers in spinal fluid and single-photon emission computed tomography as brain imaging. RESULTS: In comparing the controls and ADs, we believe that there are significant differences, with ADs having particularly low activity with regard to olfactory function and some odorants. We showed that there was a definite correlation between cognitive and olfactory function. To confirm this, we sorted subjects by markers of severity scores for comparison. In all areas, the AD group had more serious olfactory dysfunction, including in the early stages of AD. CONCLUSION: This study suggests that olfactory tests such as the Odor Stick Identification Test for the Japanese can be useful for assessing severity of AD, including cognitive dysfunction. Further investigations will enable us to establish an olfactory assessment method for the screening or diagnosis of AD.