Background Hypertension is a major risk factor for cardiovascular disease, which is a common cause of death in Zambia. Data on hypertension prevalence in Zambia are scarce and limited to specific geographic areas and/or populations. We measured hypertension prevalence among persons living with HIV (PLHIV) in Zambia using a national electronic health record (EHR) system. Methods We did a cross-sectional study of hypertension prevalence among PLHIV aged >=18 years in Zambia during 2021. Data were extracted from the SmartCare EHR, which covers ~90% of PLHIV on treatment in Zambia. PLHIV with >=2 recorded blood pressure (BP) readings in 2021 were included. Hypertension was defined as >=2 elevated BP readings (i.e., systolic BP of >=140 mmHg or diastolic BP of >=90 mmHg) during 2021 and/or on anti-hypertensive medication recorded in their EHR in the past five years. Multivariable logistic regression was used to assess associations between hypertension and independent variables. Results Among 750,098 PLHIV aged >=8 years with >=2 visits in SmartCare during 2021, 101,363 (13.5%) had >=2 blood pressure readings recorded in their EHR. Among these PLHIV, 14.7% (95% confidence interval [CI]: 14.5-14.9) had hypertension during 2021. Only 8.9% of PLHIV with hypertension had an anti-hypertensive medication recorded in their EHR. The odds of hypertension were greater in older age groups compared to PLHIV aged 18-29 years (adjusted odds ratio [aOR] for 30-44 years: 2.6 [95% CI: 2.4-2.9]; aOR for 45-49 years: 6.4 [95% CI: 5.8-7.0]; aOR for >=60 years: 14.5 [95% CI: 13.1-16.1]), urban areas (aOR: 1.9 [95% CI: 1.8-2.1]), and persons prescribed ART for >=6-month at a time (aOR: 1.1 [95% CI: 1.0-1.2]). Discussion Hypertension was common among a cohort of PLHIV in Zambia, with few having documentation of being on antihypertensive treatment. Most PLHIV were excluded from the analysis because of missing BP measurements in their EHR. Strengthening integrated management of non-communicable diseases in ART clinics might help to diagnose and treat hypertension in Zambia. Data completeness needs to be improved to routinely capture cardiovascular disease risk factors, including blood pressure readings consistently for PHLIV in their EHRs.