You've heard those hospital horror stories where the surgeon removes the wrong body part or operates on the wrong patient. Even scarier, perhaps, is a new study in the latest edition of BMJ suggesting most medical errors go unobserved, at least in the official record. In fact, the study, from doctors at Johns Hopkins, suggests medical errors may kill more people than lower respiratory diseases like emphysema and bronchitis do. That would make these medical mistakes the third leading cause of death in the United States. That would place medical errors right behind heart disease and cancer. Through their analysis of four other studies examining death rate information, the doctors estimate there are at least 251,454 deaths due to medical errors annually in the United States. The authors believe the number is actually much higher, as home and nursing home deaths are not counted in that total. This is a much greater number than a highly cited 1999 study from the Institute of Medicine that put the number in the 44,000 to 98,000 range. Other studies have put estimates closer to 195,000 deaths a year. The U.S. Department of Health and Human Services Office of the inspector general in 2008 reported 180,000 deaths by medical error among Medicare patients alone. Dr. Martin Makary and Dr. Michael Daniel, who did the study, hope their analysis will lead to real reform in a health care system they argue is letting patients down.