Between January 1973 and October 1977, 166 patients who died of breast cancer were autopsied. The examination revealed consistently more tumor involvement than had been clinically suspected. Unsuspected areas of tumor involvement included the endocrine organs (40%), lungs (28%), cardiovascular system (21%), and the genitourinary system (21%). The error in diagnosis was smaller with metastasis to the bones (10%) and central nervous system (14%). The major causes of death included pulmonary insufficiency (26%), infection (24%), cardiac disease (15%), hepatic insufficiency (14%), hemorrhage (9%), central nervous system disease (9%), and hypercalcemia (3%). The most common cause of death was metastatic disease to various organs, accounting for 42% of all deaths. Infection was the second most common cause of death; however, only 27% of the patients with infection had significant neutropenia. In patients dying of hemorrhage, only 9% were thrombocytopenic. In conclusion, although many clinicians have expressed concern that chemotherapy would add to early mortality in cancer, our study shows that this is not the case for patients with breast cancer. Deaths due to chemotherapy were rare and the rise in the infection rate did not correlate with the advent of chemotherapy.