Two hundred consecutive cases brought to the attention of a malpractice insurer by evidence of expected legal action were reviewed. Of these cases, 132 (66%) were attributed primarily to misdiagnosis, and 87 of these would have satisfied admission criteria. The most common error was grossly deficient examination relating to the chief complaint. Focused attention to physical examination and diagnostic skills, history taking, and minimal use of laboratory studies could have avoided the initiation of the majority of cases.