The novel marker special AT-rich sequence binding protein (SATB2) is highly sensitive for mesenchymal tumors with osteoblastic differentiation. However, SATB2 expression in gynecologic tract carcinosarcoma has not been previously explored. Given the potential prognostic and therapeutic implications of heterologous carcinosarcoma in the gynecologic tract, this study investigates the utility of SATB2 in identifying osteosarcomatous elements. A multi-institution database review identified consecutive cases of gynecologic tract carcinosarcoma including both heterologous and homologous types. Clinicopathologic parameters were recorded. Nuclear SATB2 immunoreactivity was scored from 1 representative whole-slide section from each case. Sixty gynecologic tract carcinosarcoma were identified (uterine corpus=47, ovary=11, fallopian tube=1, cervix=1) including 32 heterologous type (7 osteosarcoma, 3 mixed osteosarcoma/chondrosarcoma, 6 chondrosarcoma, 12 rhabdomyosarcoma, 4 mixed chondrosarcoma/rhabdomyosarcoma) and 28 homologous type. Patient ages ranged from 41 to 90 yr (average 67.9 yr). Mostly diffuse strong SATB2 positivity was present in 10/10 (100%) cases containing osteosarcoma. In these cases, SATB2 positivity was seen in malignant cells intimately associated with osteoid or bone [3/10 (30%) of these cases additionally showed patchy weak/moderate SATB2 staining in areas of nonosteogenic sarcoma elsewhere in the same tumor]. SATB2 positivity was present in 30/50 (60%) cases lacking osteosarcoma, predominantly as patchy moderate staining within undifferentiated sarcoma. No cases showed SATB2 positivity in chondrosarcoma or rhabdomyosarcoma components. SATB2 is a highly sensitive marker for osteosarcomatous differentiation in gynecologic tract carcinosarcoma, and is also highly specific when used to differentiate osteosarcoma from chondrosarcoma and rhabdomyosarcoma elements in these tumors. However, a positive SATB2 result may lack specificity for differentiating osteosarcoma from an undifferentiated sarcoma component.