This study examined patients' perceptions of medical errors by analyzing voluntary responses to an internet-based health assessment survey. Approximately 1.5% of more than 40,000 respondents reported having experienced a medical error within the past year. Patients who had a higher burden of illness were more likely to report an error, consistent with a prior study in hospitalized patients. Review by a malpractice attorney revealed that 9% of the reported errors could have been eligible for legal compensation. As the study sample consisted of voluntary respondents (not a randomly selected population), the results may not be generalizable.