Hypersensitivity to abacavir affects about 4% of patients who receive the drug for HIV-1 infection. We did a retrospective, case-control study to identify multiple markers in the vicinity of HLA-B associated with hypersensitivity reactions. HLA-B57 was present in 39 (46%) of 84 patients versus four (4%) of 113 controls (p<0 small middle dot0001). However, because of low numbers of women and other ethnic groups enrolled, these findings relate largely to white men. The lower sensitivity of HLA-B57 for predicting hypersensitivity to abacavir identified in this study compared with a previous report highlights that predictive values for markers will vary across populations. Clinical monitoring and management of hypersensitivity reactions among patients receiving abacavir must remain unchanged.