OBJECTIVE: To capture patient compliance data on a prescribed concomitant medication of an international product registry. The data needed to be collected in an accurate, timely, non-burdensome, and cost-effective manner. METHODS: Several patient compliance measurement options were considered but not selected including: physician office surveys, telephone surveys, and proxy responses. We chose the Medication Electronic Monitoring Systems (MEMS), which is a standard plastic vial, and a cap for the vial that contains a micro-electronic circuit that records times when the cap is opened and closed. MEMS bottles and caps were given to participating clinicians with specific instructions for distribution to registry participants. MEMS were to be filled with a full 6-month prescription of the concomitant medication and distributed to patients at discharge. Patients were to be instructed to complete the prescribed regimen and received instructions on the use and purpose of the MEMS. They also were to receive written instructions on returning the MEMS to their clinician after 6 months. The clinicians were to return the MEMS caps to a centralized data processing center in the United States for analysis. RESULTS: MEMS were distributed to 707 patients, by 43 physicians, in 9 countries on 6 continents. The cost of distribution (including devices and mailings) was approximately $100.00 per patient. Delays in receiving MEMS caps from patients in a timely manner were experienced, as were delays in receiving MEMS caps from sites. Of the 240 MEMS devices administered, 26% returned the cap for analysis and 24% of the MEMS caps yielded analyzable data. CONCLUSION: Compared to other methods of collecting compliance data on a large international scale, MEMS provided a non-burdensome manner for collecting data. However, the low return rate indicates that this process must be monitored closely to maximize results, minimize costs and to ensure that patient utilization does not vary.