Trisomy of chromosome 12 has been frequently described in various neoplasms, particularly in tumors of the female genitourinary tract. Fluorescence in situ hybridization with a centromeric repetitive DNA probe, specific for chromosome 12, was done to detect such cytogenic changes on frozen-tissue sections from 10 cases of ovarian sex cord stromal tumors. The case series was composed by granulosa cell tumors (four cases), fibromas (four cases), thecoma (one case), and Sertoli-Leydig cell tumor (one case). In granulosa cell tumors, the range of trisomy was 12 to 32% and in fibromas 8 to 22%, whereas in the single case of thecoma trisomy was present in 8% and in the Sertoli-Leydig cell tumor in 4% of the nuclei examined. These results represent an additional series of cases of trisomy 12 in ovarian neoplasms, namely, in ovarian sex cord stromal tumors.