To the authors' knowledge, placental site trophoblastic tumors occurring simultaneously in mother and infant have not previously been reported. The clinicopathologic features of metastatic placental site trophoblastic tumor in a mother and her 4-month-old son are described. The disease in the infant was aggressive, and he died in multiorgan failure within 5 weeks of hospital admission. Autopsy showed widespread metastases to liver, lungs, pleura, kidney, mesentery and lymph nodes. The mother, who had a uterine tumor and lung metastases, was treated with chemotherapy and hysterectomy and has no evidence of disease 26 months post-treatment. This report shows that placental site trophoblastic tumors can metastasize in both mother and child. Copyright 2002 Wiley-Liss, Inc.