Medication errors can be difficult to detect in ambulatory care, as patients or caregivers administer medications instead of health care providers. This descriptive study used home visits to children with chronic diseases to identify medication errors committed by parents, and found a remarkably high incidence of errors, particularly when parents did not use aids or support tools to help with medication administration. Although many errors were attributable to suboptimal provider–patient communication, physicians were unaware of errors in 80% of cases. An AHRQ WebM&M commentary discusses the effects of parental misunderstanding of medication instructions for their child.