Excess body weight, especially obesity, is a problem of increasing social significance, and weight gain is often correlated with age. Because physical activity can both decrease current body weight and prevent weight gain, it is an especially suitable target for behavioral intervention. A package intervention consisting of self-monitoring, goal setting, and feedback was used to increase the physical activity of healthy adults. A combined multiple-baseline and reversal design was arranged to evaluate the effects of the intervention on the number of steps taken each day by participants, as recorded by a pedometer. The intervention increased the number of steps taken across participants, but there were no changes in participant body weight during the intervention. The results suggest that a relatively simple and low-cost intervention can be used to increase the physical activity of some adults.