We have estimated the risks of ovarian and other types of cancer in first-degree relatives of women who have developed the disease (the index patients). The number of deaths from each type of cancer was determined from pedigrees taken from 391 self-referred, asymptomatic women attending a screening clinic for familial ovarian cancer. These values were compared with the expected number of deaths for women in the general population (calculated from life tables), and the relative risks were used to estimate lifetime risks. The overall relative risk were 4.5, 1.4, 1.3, and 1.1 for ovarian, stomach, breast, and endometrial cancers, respectively. The risks were invariably higher if the index patient was < 55 years old. Ovarian cancer appeared to have no clear inheritance pattern in 290 pedigrees and there was no increased risk for the first-degree relatives. Eighty-two pedigrees were compatible with a diagnosis of a multiple-site cancer family syndrome and the relative risks were 6.1, 2.8, 3.7, and 2.7 for ovarian, breast, stomach, and colorectal cancer, respectively. There was evidence of site-specific ovarian cancer in 19 families; the relative risk for the first-degree relatives was 39.1 and the lifetime risk 1 in 2. We believe that family history can be used to identify women who are at a high risk of developing ovarian and certain other types of cancer. This information can be used to counsel women attending ovarian cancer screening clinics and to maximize the usefulness of current resources.