We determined the effects of distraction on gait in healthy elderly subjects and Alzheimer's disease (AD) patients. The effects of simultaneous performance of a verbal fluency task (effect of reciting male or female names) on the time and number of steps taken to walk 30 feet were compared using a repeated-measures design with between-group comparison between community-dwelling healthy old old (oOld; n = 20; mean age +/- SD, 86 +/- 4.4), healthy young old (yOld; n = 23; mean age +/- SD, 72 +/- 3.6), and probable AD subjects without parkinsonism (n = 15; mean age +/- SD, 74 +/- 13). AD patients slowed more than the yOld (p = 0.005) and the oOld (p = 0.002). The yOld and oOld did not differ from each other (p = 0.68). Mean (+/-SD) differences in time were as follows: yOld, -2.2 +/- 1.9; oOld, -1.6 +/- 2.0; AD, -7.1 +/- 9.2 seconds. The change in steps did not differ between groups. Walking speed of AD patients slowed more than that of elderly subjects during the dual task. This may contribute to the risk of falls in AD.