Cancer was the most commonly missed diagnosis. Most errors occurred at 4 main “breakdown” points in the diagnostic process. In over half of the cases, a proper diagnostic test was not performed. Sometimes test results were not followed up adequately, or the provider did not obtain adequate information from the patient or perform an adequate physical examination. Also, providers often incorrectly interpreted results. In most cases, more than 1 breakdown and more than 1 provider contributed to a missed diagnosis. Patients also contributed to the errors in a substantial number of cases, by, for example, not providing complete information about their health or not keeping an appointment.