Delay in diagnosis of carcinoma of the breast is a significant cause of medical malpractice suits in the United States. Although less than one-third of the patients with carcinoma of the breast are less than 50 years of age, more than two-thirds of these suits involve women less than 50 years of age. To see whether or not there are medical factors that make diagnosis in young women more difficult, we reviewed all patient visits to the East Carolina University (ECU) Breast Clinic between 1 January 1988 and 30 June 1991. Women less than 50 years of age had many more patient visits (1,567 versus 838 visits) and many fewer carcinomas detected (38 versus 100 visits) than women who were more than 50 years old. The sensitivity and positive predictive value of mammography were significantly lower in young women than older women (68 versus 91 percent, p < 0.005, and 28 versus 53 percent, p < 0.001, respectively). Physical examination in young women was also less satisfactory. Tumors were more ill-defined and the percent that were easily palpable were significantly lower (45 versus 72 percent, p < 0.01). Furthermore, there was a basic difference in the reason tumors were not palpable in each age group. In older women, tumors were nonpalpable because they were small (mean size 1.0 versus 4.1 centimeters, p < 0.01), whereas in younger women, the non-palpable tumors were large (mean size 4.0 versus 3.4 centimeters), suggesting that they were not palpable because of background mammary density or diffuse growth pattern rather than size. Data from the Breast Cancer Detection Demonstration Project were analyzed and also suggested that carcinomas are more difficult to diagnose in young women. The percent of carcinomas that were not detectable by either mammogram or physical examination were inversely proportional to age and ranged from 36 percent at 40 years of age to 9 percent at 75 years of age. In addition, data from Blue Cross and Blue Shield and the ECU Breast Clinic indicated that it costs at least twice as much to diagnose each carcinoma in women less than 50 years of age. In conclusion, we believe that currently available techniques for diagnosis of carcinoma of the breast are not satisfactory for women less than 50 years of age and that this, rather than physician error, may account for the large number of malpractice suits in this age group.