We report on genomic imbalances in 19 uterine and extrauterine carcinosarcomas and comparisons with findings in 7 endometrial adenocarcinomas using comparative genomic hybridization (CGH). In the carcinosarcomas, the number of imbalances ranged from 2 to 27. Overrepresentations predominated over losses (mean, 5.8 vs 4.3) and included gains or amplifications at 8q as the single most frequent change in 15 of 19 carcinosarcomas, followed by overrepresentations at 3q (9/19), 1q (7/19), 6p (7/19), and 12p (7/19). Losses were most common at 22q (9/19), 16q (8/19), 15q (7/19), 18q (7/19), Xp (6/19), and 9q (6/19). Among 3 carcinosarcomas in which carcinomatous and sarcomatous elements could be analyzed separately, gains of 8q were identified in both components of one tumor and in the sarcomatous component of another tumor. Additional CGH analyses of 7 endometrial adenocarcinomas revealed simpler copy number changes, including recurrent gains at 8q (4/7) and 1q (4/7), suggesting a central role of 8q gains in the pathogenesis of carcinosarcomas and endometrial adenocarcinomas.