A nonrandom occurrence of trisomy 8 and of trisomy 20 in desmoid tumors has been recently reported. The finding of trisomy 8 in nondividing desmoid tumor cells by in situ hybridization prompted us to evaluate, in a similar way, the occurrence of trisomy 20 and the possible occurrence of both trisomies together because their co-existence was cytogenetically observed in a few cases. Double fluorescence in situ hybridization (FISH) with centromeric probes for chromosomes 8 and 20 was performed on 16 single cell suspensions of desmoid tumors. FISH confirmed the occurrence of trisomy 8 or 20 in a single cell suspension of desmoid tumors. Both individual trisomies, and even more their association in the same cells, are rare to extremely rare in solid tumors in general and in mesenchymal tumors in particular, and are only known to occur in infantile fibrosarcoma.