In HIV/AIDS, symptoms of depression or post-traumatic stress may interfere with important self-care behaviors such as the ability to adhere to one's medical treatment regimen. However, these problems may frequently go undetected in HIV care settings. The present study used brief self-report screening measures of depression and post-traumatic stress disorder (PTSD) in the HIV/AIDS care settings to examine (1) frequency of positive screens for these diagnoses; (2) the degree to which those with a positive screen were prescribed antidepressant treatment; and (3) the association of continuous PTSD and depression symptom scores, and categorical (screening positive or negative) PTSD and depression screening status, to each other and to ART adherence as assessed by the Medication Event Monitoring System, regardless of antidepressant treatment. Participants were 164 HIV-infected individuals who took part in a multisite adherence intervention study in HIV treatment settings in Massachusetts. Available data from 5 time points was used, yielding 444 data points. Participants screened positive for PTSD at 20% of visits, and depression at 22% of visits. At visits when participants screened positive for both depression and PTSD, 53.6% of the time they were on an antidepressant. Those who screened positive for PTSD were more likely to also screen positive for depression. In multiple regression analyses that included both continuous and dichotomous PTSD and depression and controlled for shared variance due to clustering of multiple observations, only depression contributed significant unique variance, suggesting the primary role of depression and the secondary role of PTSD in poor adherence in individuals with HIV.