Cytogenetics provides important insights into the molecular pathogenesis of human cancers. Although extensive data exist on recurring cytogenetic abnormalities in hematologic cancers, data on individual solid tumor types remain limited. Previous studies of ovarian carcinoma indicated the presence of multiple, complex clonal chromosome abnormalities. Cytogenetics remains one of a few techniques capable of detecting these multiple, simultaneously occurring genetic abnormalities. We describe cytogenetic abnormalities from a series of 244 primary ovarian cancer specimens referred to a single institution. A total of 201/244 cases had fully characterized clonal chromosome abnormalities, of which 134 showed clonal chromosome breakpoints. We used a novel statistical technique to detect nonrandom chromosome breakpoints at the level of chromosome regions. Nonrandom occurrence of chromosome breakpoints was detected at regions 1p1*, 1q1*, 1p2*, 1q2*, 1p3*, 1q3, 3p1*, 1q4*, 6q1*, 6p2, 6q2, 7p1*, 7q1, 7p2*, 11p1*, 11q1, 11q2*, 12p1, 12q2*, 13p1, and 19q1. Simultaneous occurrence of multiple abnormalities was common. However, 120/134 cases had breakpoints at one or more of 13 commonly involved regions (*), suggesting a hierarchy of genetic abnormalities. Among clinical and tumor variables that predict patient survival, tumor grade was significantly associated with the presence of chromosome breakpoints. In additional studies, we show that nonrandom chromosome abnormalities are associated with impaired survival in ovarian cancer and that specific, nonrandomly involved chromosome regions retain significant effects on survival when analyses are controlled for important clinical variables. Additional specific chromosome abnormalities in this series are described, including chromosome gains and losses in near-diploid cases and homogeneously staining regions. These results suggest that recurring, nonrandom chromosome abnormalities are important in the pathogenesis and/or progression of ovarian cancers, and target areas of the genome for molecular genetic studies.