For the first 180 years following the founding of the US, physicians occasionally were sued for medical malpractice. Allegations of negligence were errors of commission -i.e. the physician made a mistake by doing something wrong, usually mistreatment of a fracture or dislocation, a complication or death following a surgical procedure, prescribing the wrong medication, and after the discovery of the X-ray by Roentgen in 1895, causing radiation burns. In the mid twentieth century malpractice allegations slowly changed from errors of commission to errors of omission -i.e. the physician failed to do something right: almost always, failed to make a diagnosis. The number of malpractice lawsuits increased at a geometric rate beginning in the 1960s, and in the 1970s physicians began practicing defensive medicine, which lead physicians to order unnecessary radiology exams and tests. In the past 20 years the number of malpractice lawsuits has been decreasing, but the practice of defensive medicine has continued. Unnecessary exams and tests increase the likelihood of overdiagnosis and overtreatment, i.e. a new kind of error of commission.