In the elderly, gait disorders and cognitive frailty may influence each other and increase the risk of falling. The aim of the present study was to determine gait parameters in elderly people with different cognitive profiles (controls, individuals with mild cognitive impairment [MCI] and Alzheimer's disease [AD] patients) with the Locometrix three-axis accelerometer and establish whether or not this tool is more useful than conventional clinical tests (the timed "get up and go" test, the pull test and the single-leg balance test). Study subjects were all over 65, living at home and free of known gait impairments. A neuropsychological battery was applied to 14 control subjects, 14 MCI subjects and six AD patients. A motor evaluation (in single- and dual-task paradigms) was performed with three conventional clinical tests and the Locometrix (standardized gait). Our results showed that in a single-task paradigm, the Locometrix was more accurate than validated, conventional tests and generated a characteristic gait profile for each of the three cognitive profiles. In a dual-task paradigm, the gait of MCI subjects more closely resembled that of AD patients than that of control subjects. We conclude that the Locometrix is a high-performance tool for defining gait profiles, which correspond to given cognitive profiles. The use of a dual-task paradigm is a good way to screen for gait abnormalities in MCI.