Background: Recent data from large samples of healthy adolescents show that the rates of hypertension and prehypertension in adolescents are greater than expected and are increasing. Children with elevated blood pressure can develop target organ damage. This work aimed to estimate the prevalence of hypertension and to describe some related characteristics of cases in adolescent preparatory and secondary school girls of Riyadh city, KSA. Methods: A cross-sectional study conducted among a cluster sample of adolescent preparatory and secondary school girls of Riyadh city, KSA during the academic year 2016- 2017. Data collected via a predesigned and pretested questionnaire to collect the relevant data. Results: In the studied adolescent girls, 6 (3.8%) were hypertensive; previously diagnosed and on treatment, 0.6% were ex-smoker and 1.9% were smokers. Two girls (1.2%) had renal disease, 2.4% had bronchial asthma, one girl (0.6%) had hypothyroidism and 0.6% had depression. Half of the cases aged 18 years, 33.3% aged 17 years and 16.7% aged 19 years (Mean (±SD) age of cases was 15.3 (± 2.8)). Conclusion: in adolescent preparatory and secondary school girls of Riyadh city, KSA, 3.8% were hypertensive. So health-care providers should recognize the increased risk of prehypertension and hypertension and should seek to identify and manage the modifiable risk factors in those adolescent girls.