The cytogenetic abnormalities of granulosa cell tumors (GCT) of the ovary are only partially known. Up to now, mainly numerical chromosomal aberrations have been described. Therefore we performed a comprehensive study on paraffin-embedded material of 20 GCT (17 adult, 3 juvenile; patient age between 16 and 78 y) combining comparative genomic hybridization (CGH); fluorescence in situ hybridization (FISH) using DNA-specific probes for chromosome 12, 17, 22, and X; DNA cytometry; and immunohistochemistry (inhibin, p53, Ki67). By DNA cytometry, 16 of 20 tumors (80%) were diploid. However, 6 of 16 diploid tumors (37%) showed aberrations by FISH. FISH revealed monosomy 22 in 8/18 cases (40%); trisomy 12 in 5/20 (25%); monosomy X in 2/20 (10%); and loss of chromosome 17 in one case (5%). The main findings by CGH were gains of chromosomes 12 (6 cases, 33%) and 14 (6 cases, 33%) and losses of chromosomes 22 (7 cases, 35%) and X (1 case, 5%), mostly comprising whole chromosomes or chromosome arms. Inhibin and p53 were expressed in 100% and 95% of the tumors, respectively. The Ki67 index ranged from 0% to 61%. Neither immunohistochemistry, nor DNA cytometry and molecular genetic analysis, provided statistically significant prognostic information. In summary, our study reveals a distinctive pattern of cytogenetic alterations in GCT. Our observations confirm earlier reports that trisomy 12 and 14 are frequent aberrations; however, monosomy 22 seemingly is even more prevalent.