Pharmacy refill adherence has become an increasingly important measure of adherence to antiretroviral medications. It offers a simple, inexpensive, and valid method for measuring adherence. Over the past year, there have been several published developments in the use of pharmacy refill data to measure adherence. Given the utility of this adherence measurement, it is likely that pharmacy refill will be the method of choice for measuring antiretroviral adherence in an increasing number of clinical and research settings.