Joint replacement failure is usually caused by the formation of wear debris resulting in aseptic loosening. Particulate metal and soluble metal ions from orthopaedic alloys (cobalt chromium or vanadium titanium aluminium) that are used in medical prostheses can accumulate in tissues and blood leading to increased chromosome aberrations in bone marrow and peripheral blood lymphocytes. This paper demonstrates that two of the metals used in orthopaedic prostheses, chromium and vanadium can produce delayed as well as immediate effects on the chromosomes of human fibroblasts in vitro. Fibroblasts were exposed to metal ions for only 24 hours and were then expanded over 30 population doublings involving ten passages. The initial increase of chromosomal aberrations, micronuclei formation and cell loss due to lethal mutations persisted over multiple population doublings, thereby demonstrating genomic instability. Differences were seen in the reactions of normal human fibroblasts and those infected with a retrovirus carrying the cDNA encoding hTERT that rendered the normal human fibroblasts telomerase-positive and replicatively immortal. This suggests that chromosomal instability caused by metal ions is influenced by telomere length or telomerase activity. Formerly this syndrome of genomic instability has been demonstrated in two forms following irradiation. One type is non-clonal and involves the appearance of lethal aberrations that cannot have been carried by the surviving cells. The other type is clonal and the aberrations are not lethal. These may arise as a result of complex rearrangements occurring at a high rate post-insult in surviving cells. The consequences of genomic instability are not yet known but it is possible that the increase of chromosomal aberrations that have been previously observed in human patients could be due to immediate and delayed expression of cellular damage after exposure to orthopaedic metals.