To investigate the frequency of numerical aberrations of chromosomes 7, X and Y in patients with osteoarthritis (OA) by performing fluorescent in situ hybridization (FISH) studies on articular cartilage, and to correlate the chromosomal changes with the degree and location of articular involvement.Thirty-four women and 10 men with OA were included in the study. As a control group, 6 women and 5 men operated for orthopedic disorders other than OA were analyzed.FISH studies were performed on hip or knee cartilage, using two-color centromere-specific probes for chromosomes 7 & X for women and 7 & Y for men.FISH analysis revealed that 46% of OA patients had numerical abnormalities of chromosomes 7, X or Y. An extra chromosome 7 (trisomy 7) was present in 35% of patients with chromosomal aberrations. All males with OA lost the Y chromosome while 15% of the women had loss of one chromosome X (monosomy X). Trisomy 7 was associated with hip OA (p=0.019) and advanced OA according to the Kellgren and Lawrence classification (p=0.05). None of the 11 controls showed abnormalities in the chromosomes analyzed.FISH analysis showed the presence of numerical chromosomal abnormalities in the articular cartilage of patients with OA.