Primary peritoneal adenosarcoma with sarcomatous overgrowth and fetal-type cartilage presented in a 48-year-old female patient is described. The tumor seems likely to have derived from the pelvic peritoneum, wheareas the uterus, ovaries and tubes were uninvolved. It was composed of benign-appearing glands and a sarcomatous component showing cartilaginous differentiation. The extrauterine adenosarcomas were reported in other sites, e.g. cervix, ovary, fallopian tube, bladder, and peritoneum. This case was the ninth case of the primary peritoneal adenosarcoma in the English literature and the first report in Thailand.

Keywords: Peritoneal adenosarcoma, Stromal overgrowth, Fetal-type cartilage, Mixedmesodermal tumor