This study compared the efficacy of two low-cost interventions for physical activity adoption. Sedentary (N = 194) adults recruited through newspaper advertisements were randomized to receive either a motivationally-matched, individually-tailored intervention (IT) or a standard self-help intervention (ST). Assessments and interventions were delivered by repeated mailings at baseline, one, three, and six months. Participants were assessed regarding current physical activity behavior, motivational readiness to adopt regular physical activity, and psychological constructs associated with physical activity participation (e.g. self-efficacy, decisional balance). Repeated measures analyses of variance (ANOVAs) revealed significant increases in physical activity participation between baseline and six months for both groups with a significantly greater increase among IT participants. The IT group outperformed the ST group on all primary outcome measures: (a) minutes of physical activity per week, (b) reaching Centers for Disease Control and American College of Sports Medicine (CDC/ACSM) recommended minimum physical activity criteria, and (c) achieving the Action stage of motivational readiness for physical activity adoption. Both groups showed significant improvement between baseline and six months on the psychological constructs associated with physical activity adoption (e.g. self-efficacy), with no significant differences observed between the treatment groups. Utilizing computer expert systems and self-help manuals to provide individually-tailored, motivationally-matched interventions appears to be an effective, low-cost approach for enhancing physical activity participation in the community.