Resumo. BACKGROUND: Motor performance in older adults with cognitive impairment is worse under dual task conditions, increasing the risk of falls. However, there is a lack of studies that analyze this performance over time in people with different cognitive profiles. AIM: This study aimed to compare the performance of an isolated task and a dual task in people with preserved cognition (PrC), mild cognitive impairment (MCI) and Alzheimer`s disease (AD). METHOD: Data were collected on two occasions (T1; T2), thirty-two months apart. Participants (n=51) were separated between groups: PrC (n=22), MCI (n=19) and AD (n=10). They were analyzed in three situations: 1) isolated motor task - Timed up and go test (TUGT); 2) cognitive-motor test (CMT)– dialing on the phone; 3) dual task (DT). To compare the performance of the dual task between the groups, delta was calculated and the ANCOVA test was applied. RESULTS: Although the cost of the dual task was not significantly different over time in any group, we found increases in the time required to complete the TUGT (p<0.01) and TUGT-DT (p>0.01) after 32 months in the AD group and a reduction in time in the PrC and MCI groups.  A greater number of steps in the TUGT-DT (p<0.01) and an increase in cadence in the TUGT (p=0.01) and TUGT-DT (p<0.01) were also found in the AD group. CONCLUSION:We suggest that a more functional task, such as walking while typing on the phone, may be considered a more sensitive way of assessing older adults with AD.