BACKGROUND፡ The aim of this study was to estimate the prevalence and to determine the associated factors of undiagnosed depression amongst hypertensive patients (HTNP) at primary health care centers (PHCC) in Gaza.METHODS: A cross-sectional survey was conducted including 538 HTNP as a recruitment phase of a clustered randomized controlled trial. Data were collected through face-to-face structured interview, and depression status was assessed by Beck's Depression Inventory (BDI-II). Data were analyzed by STATA version 14 using standard complex survey analyses, accounted for unresponsiveness and clustering approach. Generalized linear regression analysis was performed to assess associations.RESULTS: The prevalence of undiagnosed clinical depression was 11.6% (95% confidence interval [CI]: 8.1, 16.3). Moreover, prevalence of 15.4% (95% CI: 10.8, 21.6) was found for mild depression symptoms. We found that non-adherence to antihypertensive medications (AHTNM) (β = 0.9, 95% CI: 0.17, 1.7), having more health-care system support (β = 2.8, 95% CI: 1.6, 3.9) and number of AHTNM (β = 1.5, 95% CI: 0.6, 2.5) remain significantly positively associated with BDI-II score. On the other hand, older age (β = -0.1, 95% CI: -0.2, -0.02), having better social support (β = -6.8, 95% CI: -8.9, -4.7) and having stronger patient-doctor relationship (β = -4.1, 95% CI: -6.9, -1.2) kept significantly negative association.CONCLUSION: The prevalence of undiagnosed depression was about one-quarter of all cases; half of them were moderate to severe. Routine screening of depression status should be a part of the care of HTNP in PHCC.KEYWORDS:  Hypertension; Depression; Prevalence; Medication adherence.