Researchers designing clinical trials often specify usual care received by participants as the control condition expecting that all participants receive usual care regardless of group assignment. The assumption is that the groups in the study are affected similarly. We describe the assessment of usual care within the 16 studies in Multisite Adherence Collaboration in HIV (MACH 14), a multisite collaboration on adherence to antiretroviral therapy. Only five of the studies in MACH 14 assessed usual care. Assessment protocols varied as did the timing and frequency of assessments. All usual care assessments addressed patient education focused on HIV, HIV medications, and medication adherence. Our findings support earlier work that calls for systematic assessments of usual care within the study design, inclusion of descriptions of usual care in reports of the study, and the influence of usual care on the experimental condition in clinical trials.