The objective was to estimate the duration of the effects of aerobic exercise on mood. Healthy men (n = 13) and women (n = 35) ages 18 to 25 years (M = 20.2, SD = 3.4) were randomly assigned to either a control or exercise group. Participants completed the Profile of Mood States before, after, and at 1, 2, 4, 8, 12, and 24 hours following either exercise at 60% VO2 peak or quiet rest. Repeated-measures analysis of covariance was utilized with VO2 peak entered as a covariate. The exercise group showed significantly lower total mood disturbance immediately after and at 4, 8, and 12 hours following exercise.