Cytogenetic studies of ovarian sex cord stromal cell tumors, although limited in number, have found trisomy 12 to be a recurring abnormality, especially in fibromas and granulosa cell tumors (GCTs). However, recent fluorescence in situ hybridization (FISH) studies have failed to confirm a high prevalence of trisomy 12 in GCTs. We describe the karyotypic findings in one adult and one juvenile GCT. Only the juvenile GCT had an extra, abnormal chromosome 12, but both the adult and juvenile GCT had monosomy 22. In light of these findings and the data in the literature, we suggest that monosomy 22 may be important in the genesis of these relatively rare tumors.