The association between patient sex and the tolerability of antiretroviral drugs (ARVs) is increasingly being recognized. Several lines of evidence suggest that women are more likely than men to develop side effects to ARVs. On the other hand, it has been generally accepted that the efficacies of the ARVs are similar in both sexes. However, recent studies suggest that this may not always be the case. In addition to these observed sex-related differences in the effects of ARVs, there is growing evidence that the pharmacokinetic profile of some of these drugs may be different among male and female HIV infected patients.