Providing anti-retroviral therapy (ART) to patients free of charge enhances their wellbeing, reduces the number of opportunistic infections and enables them to live productive lives, but only if these drugs are taken regularly every day for the rest of their lives. Patients' ART adherence levels are difficult and expensive to estimate. If simple available measures, such as pharmacy refill records, could be correlated with laboratory test results for improved CD4 counts (indicating immunological recovery) and decreased viral loads (VLs--indicating virological recovery), these could be used as preliminary measures of adherence. The objective was to determine whether the combination of pharmacy refill records and pill counts (including counts for all medications in the HAART regimen) could predict immunological and virologic responses through increased CD4 cell counts and suppressed VL. Correlations were compiled for patients' pharmacy refill records, pill counts, CD4 cell counts, VL counts and self-reported ART adherence at one clinic in Gaborone, Botswana. There was a weak positive, relationship between ART adherence, CD4 cell counts and VL. Pharmacy refills and pill counts adherence measurement methodologies scored high on sensitivity and positive predictive values. Pharmacy refill records and pill counts are useful indicators of patients' ART adherence levels, but should be supplemented with CD4 and VL counts at regular intervals. Copyright © 2011 Elsevier Ltd. All rights reserved.