There have been recent increases in the number of female participants in HIV clinical trials and the number of studies addressing the influence of sex on HIV infection. The findings of some studies indicate a potential sex differences in the frequency and severity of adverse reactions to antiretroviral drugs. This article reviews the available data on the incidence and characteristics of potential sex differences in adverse reactions to certain nucleoside and nonnucleoside reverse transcriptase inhibitors and protease inhibitors. Adverse effects for which a sex difference has been reported include lactic acidosis, rash, elevation in liver enzymes, dyslipidemia, and insulin resistance. The reasons for these sex differences in adverse drug events are unclear but may include differences between men and women in body mass index and fat composition, hormonal effects on drug metabolism, or the effects of genomic constitutional differences on the levels of various enzymes. These differences warrant further study.