Many health systems rely on telephone triage to determine the urgency with which a patient should be seen by a clinician. Prior research has demonstrated that errors in triage may lead to patient harm. In this study, standardized patients with a variety of symptoms contacted telephone triage nurses at four Dutch general practices. The investigators analyzed the accuracy of triage decisions by comparing the nurses' advice to the national guideline for telephone triage. Both underestimation and overestimation of the severity of patients' illnesses occurred, although errors were less frequent when nurses had received specific training in use of the guideline. A prior AHRQ WebM&M commentary discusses the potential pitfalls inherent to providing medical advice by telephone and strategies for minimizing patient harm in these situations.