The metastatic sites of infiltrating duct (IDC) and infiltrating lobular carcinoma (ILC) have been compared using both clinical and autopsy data. The following statistically significant differences were found: Lung parenchymal metastases were more common in IDC. Bone trephine biopsies were more likely to be positive in ILC. Carcinomatous meningitis was associated almost exclusively with ILC. Peritoneal/retroperitoneal metastases of distinctive pattern occurred in ILC. There was often associated linitis plastica-like involvement of the stomach wall and diffuse infiltration of the uterus. Hydronephrosis was a common secondary phenomenon.