Prevalence estimates for high blood pressure (BP) among adolescents in sub-Saharan Africa vary widely and most studies have relied on attended automated office BP (AOBP) measurements. We aimed to estimate prevalence of high BP using unattended AOBP followed by 24-Hour ambulatory BP monitoring (24-Hour ABPM) for confirmation and to determine factors associated with confirmed high BP. Between April and August 2018, 500 adolescents aged 11 to 15 years were enrolled from three randomly selected public schools in Mwanza city (Tanzania) to participate in a 2-year prospective cohort study. We obtained three consecutive unattended AOBP measurements. Follow-up AOBP measurements were obtained in participants with high BP at initial measurements. Participants whose follow-up measurements remained high underwent 24-Hour ABPM. Of all 500 participants, 36.6% had high BP using first AOBP measurement; 25.6% using average of the second and third AOBP measurements and 10.2% using average of follow-up AOBP measurements and were eligible for 24-Hour ABPM. Only 13(2.6%) had confirmed high BP and they had no unique distinguishing characteristic. White coat hypertension is common among adolescents in Africa. Cardiovascular health promotion in Africa can be done through school-based screening for high BP among adolescents using one unattended AOBP