In 25 years, 18 patients with breast cancer were treated at St Jude Children's Research Hospital, 16 were female and 2 were male. The patients presented with primary malignancy (2), metastatic disease (13), or secondary malignancy (3). One of the females with primary breast malignancy had alveolar rhabdomyosarcoma. She was treated with wide excision and is currently receiving chemotherapy. The other patient presented with non-Hodgkin's lymphoma of the right breast. After biopsy, she was treated with chemotherapy. Of 13 patients with metastatic disease, the primary lesion was rhabdomyosarcoma in nine. One patient each had non-Hodgkin's lymphoma, Hodgkin's lymphoma, neuroblastoma, and signet-cell adenocarcinoma. All patients with metastatic disease to the breast died of the disease. Three females presented with invasive ductal carcinoma of the breast after treatment for Hodgkin's disease. Two underwent mastectomy and are alive without evidence of disease. One patient refused therapy and died of the second malignancy. We conclude that (1) breast malignancies had three distinctly different presentations in our patients, (2) the breasts of pediatric oncology patients should be carefully and routinely examined for metastatic disease, and (3) metastatic disease in the breast of a child is a manifestation of disseminated disease and is associated with an extremely poor prognosis. © 1994.