The evidence from the 4 epidemiologic studies published before mid 1995, which have investigated the incidence of cancers in patients who have undergone joint implants, is conflicting. The results of the 2 earlier studies suggested a sustained increase in the risk of lymphoma and leukemia after total hip arthroplasty. The results of the 2 more recent studies have not confirmed this, although in 1 study an increased risk was observed in the first year after implantation. The heterogeneity may be statistical in origin, but could also have a biologic explanation in the greater proportion of metal on metal prostheses used before 1973. All 4 studies used national data as the comparison. Here are presented the results of 2 matched cohort studies and a case control study set in North America and Scotland, and an overview of the 4 previous studies. Neither the results of the matched studies of patients operated on after 1973 nor the results of the latter 2 published studies suggest an increased risk of lymphoma or leukemia. If metal on metal articulations are reintroduced, careful surveillance is essential.