A family is presented in whom hereditary angioedema (HAE) and hereditary breast cancer were coexistent, an association not previously reported. A potential for genetic and treatment-related interactions between the two conditions exists. The use of the hormonal agent danazol to suppress HAE is unlikely to adversely affect the development or outcome of breast cancer. Surgery, chemotheraphy, and radiotherapy were received by affected family members, without triggering edema. Whether hormonal breast cancer treatment affects the suppression of HAE by remains unknown.