BACKGROUND: Gait disorders caused by dementia have been associated with frontal lobe dysfunction. Dual-tasking is used to explore the involvement of cortical level in gait control. It has been shown that dual-task induced gait changes that could be related to (1) the efficiency of executive function, (2) the level of difficulty involved in the walking-associated task, or (3) the articulo-motor components comprised in the walking-associated task. A better understanding of dual-task related changes in demented subjects with frontal lobe dysfunction could help us to clarify the role of the frontal lobe in motor gait control. OBJECTIVE: To assess and compare the effects of two mental arithmetic tasks involving similar articulo-motor components but different level of difficulty on the mean values and coefficient of variation (CV) of stride time among demented older adults with impaired executive function. METHODS: The mean values and coefficients of variation of stride time were measured using a GAITRite((R))-System among 16 demented older adults with impaired executive function while walking with and without forward counting (FC) and backward counting (BC). RESULTS: The mean values and CV of stride time were significantly higher under both dual-task conditions than during a simple walking task (p<0.05). The change in CV of stride time during BC was significantly higher when compared with the change during FC (p=0.015), whereas the change in mean value was not significant (p=0.056). There was no difference between the dual-task and single task condition as far the number of enumerated figures were concerned (p=0.678 for FC and p=0.069 for BC), but significantly fewer figures were enumerated while BC compared with FC (p<0.001). CONCLUSION: BC provoked more changes in gait parameters than FC with major modification in gait variability related to an inappropriate focusing of attention. These findings suggest that the CV may be a suitable criterion for the assessment of gait control.