Cytogenetic analysis has become an important part of the diagnostic evaluation of most hematological neoplasms. However, there is limited information on the value of cytogenetic analysis in most solid tumors, including cerebral astrocytomas. This report summarizes a prospective cytogenetic study of 99 human cerebral astrocytomas, 16 mixed oligoastrocytomas, and 2 gliosarcomas. The cytogenetic procedure involved in situ culture and robotic harvesting techniques. Correlative clinical and survival data were available on all patients. We successfully cultured and obtained suitable metaphases in 107 of the 117 tumors. One or more chromosomally abnormal clones were observed in 72 tumors, and nonclonal or normal karyotypes were observed in 35 tumors. In a multivariate analysis, survival time was significantly better in patients whose tumors had normal or nonclonal karyotypes on cytogenetic analyses than in those whose tumors had clonal abnormalities (p = 0.0071). Our study demonstrates that cytogenetic analysis provides independent prognostic information in patients with cerebral astrocytomas.