INTRODUCTION: Although evidence exists that adolescents' hypertension could lead to adults' hypertension, it is a general belief that measures for early detection and treatment of this condition is seldom undertaken especially in medically underserved communities such as Maiduguri, Northeastern Nigeria. This study investigated the prevalence of undiagnosed hypertension among adolescents in Maiduguri, Nigeria, and explored the association between undiagnosed hypertension and adolescents' physical characteristics and parental socio-demographic factors. METHODS: Participants' physical characteristics were assessed, and information on their socio-demographics including parental socioeconomic status were obtained. Blood pressures and heart rates of the participants were also measured three times at 5-10-min period. RESULTS: The prevalence of undiagnosed hypertension among the students was 13.2 %, and overwhelming majority (82.4 %) of the hypertensive students were in the prehypertensive stage, while 17.6 % were in the stage 1 classification of hypertension. Higher prevalence of undiagnosed hypertension was observed for the females compared to the male adolescents (chi2 = 15.49, p = 0.001), and presence of undiagnosed hypertension is positively but tenuously linked to age (r = 0.11, p = 0.01), body mass index (r = 0.10, p = 0.01), and parental income (r = 0.26, p = 0.02) of the students. DISCUSSION: This study suggests that any effective programs designed to mitigate undiagnosed hypertension among adolescents in this city should include strategies that address possible barriers to physical activity and exercise among female adolescents in the society.