To determine objectively the patient and physician factors that lead to breast cancer malpractice litigation, a review was undertaken of all cases tried in the US federal and state civil court system over a 20-year period from 1971 through 1990. Forty-five cases were identified and all involved a delayed diagnosis of breast cancer (the mean delay was 15 months). The patients were young (mean age, 40 years). Of 45 cases studied, the majority of patients (37 [82%]) found a painless mass by self-examination of the breast. Only 22 patients (49%) had further workup, mostly by mammography (20 [44%]). The results of 16 mammograms (80%) were read as normal. Obstetricians and gynecologists were involved in the greatest number of cases (21 [50%]), followed by family practitioners and internists (17 [41%]), general surgeons (12 [28%]), and radiologists (4 [10%]).