Data on the association of ovarian cancer with other cancers in families are limited, and no data are available on the involvement of specific morphological types. The nationwide Swedish Family-Cancer Database on 10.2 million individuals and 19175 invasive ovarian cancers was used to calculate standardised incidence ratios (SIRs) and 95% confidence intervals (CIs) for familial ovarian cancer in 0-66-year-old daughters when mothers or sisters were affected. The SIR for concordant ovarian cancers was increased. When the mother or sister had breast cancer, the SIRs were 1.21 and 1.48, respectively; when they had endometrial cancer, the SIRs were 1.45 and 2.53. Multiple myeloma in the mother was associated with a risk of ovarian cancer in the daughter. The risk of endometrioid ovarian cancer was 3.40 in the daughter when the mother presented with endometrial cancer. Our data show a strong familial coupling of ovarian and endometrial cancers, which appears to be specific to the endometrioid morphology.