Interruptions are inevitable for busy clinicians, and recently studies have shown that interruptions can increase workload for physicians and raise the risk of medication administration errors by nurses. However, these safety risks must be balanced against the fact that interruptions are often necessary for patient care. This study analyzed data from telephone logs and a formal quality assurance program to examine the effect of telephone interruptions on accuracy of on-call radiology residents' study interpretations. The authors found that a higher frequency of interruptions was associated with more diagnostic errors. This study is one of the first to document clinical consequences of physician interruptions and adds to our understanding of systems contributors to diagnostic errors. An incident involving an incorrect overnight radiology interpretation is discussed in a past AHRQ WebM&M commentary.