We performed interphase in situ hybridization (ISH) for chromosomes 12 and X and now cytometric DNA analysis on seven juvenile granulosa cell tumors to verify this observation and correlate the results with clinicopathologic factors. Five cases were primary ovarian tumors and two were metastatic lesions. Our results show that four tumors exhibited polysomy 12 and four had monosomy X; only two tumors displayed concurrent aberrations of both chromosomes. Of the six tumors with interpretable flow cytometric histograms three showed DNA aneuploidy and three were DNA diploid. All three aneuploid tumors manifested polysomy 12. Of the three diploid DNA neoplasms two showed monosomy X and one displayed disomy for chromosomes 12 and X. No apparent correlation between numerical chromosomal abnormalities and the biological course was observed in this small cohort. Our results indicate that chromosomes 12 and X are frequently altered in these neoplasms and thus could be targeted for further molecular studies in order to identify genetic aberrations which might be associated with JGCT tumorigenesis.