Past research has demonstrated that health behavior is correlated with time perspective: long-term thinkers are more likely than short-term thinkers to engage in health protective behaviors and less likely to engage in health damaging behaviors. To date, however, no research has experimentally demonstrated that time perspective is causally related to health behavior. We designed a brief (three 1/2-h weekly sessions) time perspective intervention to enhance long-term thinking about physical activity and examined its efficacy among two samples of young adults who signed up for fitness classes at a university recreational facility. Participants were assigned to one of three conditions: time perspective intervention, goal-setting control intervention, and no-treatment control. In Study 1, physical activity levels were assessed at preintervention, at postintervention (3 weeks later), and at 10-week follow-up (7 weeks after completion of the intervention). Controlling for preintervention physical activity levels, time perspective participants reported increased levels of physical activity relative to both other groups at postintervention, and relative to the no-treatment group at 10-week follow-up. This study provides the first experimental evidence that the effects of health behavior interventions may be enhanced by increasing participants’ long-term time perspective, and that time perspective is causally associated with health behavior. Study 2 replicated some of the effects of Study 1 using a larger sample, a six-month follow-up interval, and improved measurement of outcome. Together Studies 1 and 2 suggest that time perspective is an important ingredient in interventions designed to promote physical activity.