UNLABELLED: We aimed to assess the prevalence of resistant hypertension (RH) in patients attending hypertension outpatient clinics and to identify risk factors for RH. We studied the medical records of the last visit of all patients (n = 1810; 40.4% males, age 56.5 ± 13.5 years) who attended at least once our hypertension outpatient clinic during the last decade. RH was defined as blood pressure (BP) > 140/90 mmHg in patients without diabetes or chronic kidney disease (or BP > 130/80 mmHg in patients with the latter diseases) despite treatment with full doses of three antihypertensive agents from different classes or controlled BP on four or more different antihypertensive agents. The prevalence of RH was 12.3%, whereas 22.2% of the patients had well-controlled hypertension and 65.5% had uncontrolled hypertension but were on less than three antihypertensive agents. Independent predictors of RH were age (risk ratio, RR = 1.08, 95% confidence interval, CI 1.05-1.12, p < 0.001), body mass index (RR = 1.06, 95% CI 1.00-1.13, p < 0.05) and the presence of the metabolic syndrome (MetS) (RR = 2.01, 95% CI 1.03-3.91, p < 0.05).CONCLUSIONS: RH is frequent in patients followed up in hypertension outpatient clinics. In addition to age and obesity, MetS appears to be associated with increased risk for RH. Clarification of the mechanisms underpinning the association between MetS and hypertension might reduce the prevalence of RH.