Sertoli-Leydig cell tumors (SLCTs) represent a rare group of sex-cord stromal tumors of the ovary of unknown pathogenesis. We report a SLCT of intermediate differentiation with peritoneal recurrence and lymph node metastasis 12 months after removal, including cytogenetic analysis by comparative genomic hybridization and fluorescence in situ hybridization, which showed trisomy 8 as sole unbalanced karyotypic aberration. Our results provide evidence that a simple numeric chromosomal abnormality in SLCT may be associated with a malignant phenotype and suggest that the molecular pathogenesis of SLCT may be different from ovarian granulosa-stromal cell tumors.