Telephone communication with patients is common in ambulatory practice, but accurately gauging illness severity and formulating an appropriate plan of action may be difficult, leading to potential patient safety issues. This study analyzed telephone-related closed malpractice claims from a large insurance company database in order to elucidate specific types of errors and contributing factors. Most cases alleged that clinicians failed to accurately diagnose the patient; types of errors leading to misdiagnosis included inadequate documentation, faulty triage, and lack of protocols for handling telephone calls. A diagnostic error due to faulty telephone triage is discussed in this AHRQ WebM&M case, and a prior commentary offers practical tips for improving patient triage and management by telephone.