This study assessed the ability of patients to detect medical errors through an innovative mechanism of using patient safety liaisons (trained patient and family volunteers) to conduct interviews of patients at an outpatient chemotherapy center. Patients' responses to open-ended questions were reviewed by physicians, who classified reported adverse events as adverse events, near misses, or problems with service quality (eg, delays or poor communication). Patients demonstrated good understanding of safe practices in outpatient chemotherapy, and nearly one-fourth of the patients felt they had experienced unsafe care. However, only 1% of the reported events were classified as true medical errors with potential for harm. The vast majority of events related to service quality rather than quality of care. Prior research also assessed the relationship between patient perceptions of care quality and service quality.