Twenty-four old (M = 70.9 years) and 24 young (M = 21.7 years) adults performed a mental rotation task in which stimuli were pairs of three-dimensional objects (toy cowboy figures). Participants were presented with one pair of figures on each trial and were required to make a "yes/no" decision as to whether the figures were in identical ("yes") or mirror image ("no") poses. A significant interactive effect of age and rotation angle on response time suggested slower rates of mental rotation for old vs. young adults, as did significant age differences in mean slope and intercept values based on individual subjects' linear equations for response time over rotation angle. Findings were consistent with those of previous studies which have reported significant age-related slowing in mental rotation.