Adherence to antiretroviral therapy is a powerful predictor of response to therapy. For optimal antiretroviral therapy response, individuals need to take more than 95% of their prescribed medication. The most widely used method for measuring adherence is self-report of the number of missed doses and this should be done at every clinic visit. There are several well-recognized predictors of poor adherence, such as illicit drug use, depression, limited knowledge or ambivalence about starting treatment. Adherence can be improved by addressing these issues or through other means such as pill boxes or electronic reminders.