Using judgments obtained in interviews with 33 Massachusetts physicians, the annual statewide volume of expenditures incurred for defensive medical reasons in 1982 was estimated to be $1.0 billion, 12% of all medical care expenditures. Estimates for the nation were $37 billion, 14% of expenditures. Nationally, 180,000 cesarean deliveries were thought to be performed for defensive motives. In their own institutions, respondents judged 43% of all skull x-rays following injury to be medically justified, 30% to be defensive medicine, 16% to be placebos, and 11% to be physician misjudgments. In considering the economic and noneconomic costs of medical malpractice procedures, the dollar costs of insurance were considered most serious, followed closely by defensive medicine, unfairness, and poorer relations with patients. Thirty-two percent of the responsibility for the negative aspects of malpractice processes was assigned to lawyers, 21% to physicians, 18% to legislatures and courts, 16% to patients, and 13% to insurance companies.