OBJECTIVES. The authors compared judgments of the population risks of invasive cardiac procedures made by cardiologists and other internal medicine physicians. Our main hypotheses were that cardiologists' judgments would differ from those made by the other physicians and that cardiologists' judgments would be more accurate than those of other physicians. METHODS. This was a cross-sectional survey of senior staff and physician-trainees at two teaching hospitals affiliated with a US medical school, Emergency Department physicians at a community hospital in the same metropolitan area, and senior staff and trainees at two teaching hospitals affiliated with a UK school. Judgments of the risks of severe morbidity and death due to Swan-Ganz catheterization, cardiac catheterization, percutaneous coronary angioplasty, and coronary artery bypass grafting were assessed. RESULTS. Nineteen cardiologists judged the risks of severe morbidity due to all procedures and the risks of death due to all procedures except coronary artery bypass grafting to be significantly lower than did the 78 other internists. Cardiologists more frequently made accurate judgments of the rates of morbidity and death due to cardiac catheterization than did the other internists; other internists more frequently made accurate judgments for the rates of morbidity due to Swan-Ganz catheterization. CONCLUSIONS. Disagreements about the risks of procedures may arise from a paucity of published data, or from an over-supply of confusing data.