This study examined whether adherence to a lifestyle physical activity intervention predicted weekly participation in at least 150 min of moderate to vigorous physical activity among 244 sedentary healthy adults. Structural equation modeling was used to assess the association between adherence and physical activity. Markers of adherence were attendance, homework completion, and self-monitoring for a group-based intervention and telephone call completion, homework completion, and self-monitoring for a telephone and mail-delivered intervention. For both interventions, adherence significantly predicted moderate to vigorous physical activity. Adherence to lifestyle physical activity interventions ought to be encouraged to increase the likelihood that participants will engage in an adequate amount of physical activity for health benefits to occur.