Missed follow-up of abnormal test results and resultant delays in diagnosis is a safety issue that is gaining increasing attention. Despite increases in the numbers and types of available diagnostic tests, current systems in health care do not reliably ensure that test results are received and acted upon by ordering physicians. This article examines the case of a patient whose diagnosis of tuberculosis was substantially delayed because of systems problems, including poor continuity (with multiple-provider involvement), lack of communication of test results and other clinical information, and several handoffs. Strategies to ensure adequate communication of critical information and follow-up of test results are discussed, such as explicit criteria for communication of abnormal results, test-tracking systems for ordering providers, and use of information technologies.