Resistant hypertension is common among the hypertensive population with reported prevalence of 12 to 15%. These patients have a higher cardiovascular risk and consequently a poorer cardiovascular prognosis. Suboptimal adherence with antihypertensive medication is a common contributing factor in apparent treatment-resistant hypertension. Patients were observed taking their medications under direct supervision at our directly observed therapy (DOT) clinic. At the DOT clinic visit, patients were fitted with a 24-h ambulatory blood pressure (ABP) monitor and each drug, at currently prescribed dose, was administered by a nurse; at an hourly interval and patient observed for 7 h. ABP readings between pre and post DOT clinic were compared. Fifty out of 56 patients had complete data on the ABP. Twenty four were female and the mean (s.d.) age was 62.0 (11.0) years. On the basis of the study methods that differentiated patients according to their BP response during the DOT clinic, twenty-five (50.0%) patients were deemed to be truly resistant (24-h ambulatory systolic blood pressure (SBP) fall <5 mm Hg) and the remaining 25 were deemed to have clinically significant non-adherence (24-h ambulatory SBP fall ⩾5 mm Hg) to prescribed therapy. In non-adherent patients, the mean 24-h ambulatory BP drop observed was 19.5/9.4 mm Hg (P<0.001 for both). Our results suggest that non-adherence is very common among patients considered to have apparent treatment-resistant hypertension. DOT clinic can be an effective method of identifying the truly resistant hypertensive patients.