OBJECTIVES: Determine if self-monitoring of physical activity using wearable physical activity trackers (Garmin, Fitbit, etc.) affects member health care costs and utilization. METHODS: Analyzed administrative claims of 1,258 health plan members by their length of tracker usage (3+ months, 6+ months, 9+ months and 12+ months). Compared the cost and count of members’ emergency room, office, inpatient and outpatient visits before and after they received trackers, and the percent of costs attributable to preventive services. RESULTS: Office visits increased 8% for members who used the devices 9+ months, and 11% for those who used them 12+ months. Total costs increased 27% in the 12+ month tracker usage group. Preventive service office visits increased 16% for the 9+ month group and 14% for the 12+ month tracker group. In addition, the total cost of preventive office visits increased 13% for those who monitored their physical activity with trackers for at least 9 months, and 13% for those who monitored their physical activity for at least 12 months. CONCLUSIONS: Providing trackers to health plan members increased usage and spending on health care services, including preventive health services, in the 12-month period that followed. Follow-up research is needed to determine if an increase in preventive service visits, associated with tracker usage, drives down the need for costly ER and inpatient visits.