Poor care coordination has been shown to be a risk factor for preventable errors in the ambulatory setting, and patients consistently voice concern about care coordination problems. This survey, which builds on prior Commonwealth Fund reports, found that care coordination was a major determinant of patient-reported medication errors in all seven countries studied. The study reinforces the role of health systems in ambulatory patient safety, and the need for improved communication between providers and better integration of health systems to reduce preventable errors for outpatients.