IntroductionNamibia has the highest burden and incidence of hypertension in sub-Sahara Africa. Though non-adherence to antihypertensive therapy is an important cardiovascular risk factor, little is known about potential ways to improve adherence in Namibia following universal access. The objective of this study is to validate the Hill-Bone compliance scale and determine the level and predictors of adherence to antihypertensive treatment in primary health care settings in sub-urban townships of Windhoek, Namibia.MethodsReliability was determined by Cronbach’s alpha. Principal component analysis (PCA) was used to assess construct validity.ResultsThe PCA was consistent with the three constructs for 12 items, explaining 24.1, 16.7 and 10.8% of the variance. Cronbach’s alpha was 0.695. None of the 120 patients had perfect adherence to antihypertensive therapy, and less than half had acceptable levels of adherence (≥ 80%). The mean adherence level was 76.7 ± 8.1%. Three quarters of patients ever missed their scheduled clinic appointment. Having a family support system (OR = 5.4, 95% CI 1.687–27.6, p = 0.045) and attendance of follow-up visits (OR = 3.1, 95% CI 1.1–8.7, p = 0.03) were significant predictors of adherence. Having HIV/AIDs did not lower adherence.ConclusionsThe modified Namibian version of the Hill-Bone scale is reliable and valid for assessing adherence to antihypertensives in Namibia. There is sub-optimal adherence to antihypertensive therapy among primary health cares in Namibia. This needs standardized systems to strengthen adherence monitoring as well as investigation of other factors including transport to take full advantage of universal access.