Objective Hypertension contributes to increased risk of cardiovascular disease in patients with Turner syndrome (TS). Our objective was to evaluate blood pressure (BP) in girls with TS followed longitudinally through childhood and adolescence compared to a newly established BP reference material. Design Cohort study with data collected from 1991 to 2019 consisting of a population-based reference cohort and a group of girls with TS followed at a single tertiary centre. Patients/Participants Reference population of 1888 healthy girls with 4890 BP recordings and 60 girls with TS with 365 BP recordings. Measurements Difference in diastolic BP (DBP) and systolic BP (SBP), expressed in standard deviation scores (SDS), between girls with TS and the reference population, unadjusted and adjusted for BMI. Difference in BP (SDS) between TS subgroups (karyotype, oestrogen treatment, cardiac diagnosis). Results The girls with TS had significantly higher DBP (mean +/- SD, 0.72 SDS +/- 0.95; p < .001) and SBP (0.53 SDS +/- 1.11; p = .001) than the reference population. Adjusted for BMI, girls with TS had significantly higher DBP (mean +/- SE, 0.71 SDS +/- 0.12; p < .001) but not SBP (0.17 SDS +/- 0.16; p = .29). There was no significant difference in DBP (median, IQR: 0.97 SDS, 0.30-1.58 vs. 0.76 SDS, 0.10-1.20; p = .31) or SBP (0.51 SDS, 0.15-1.30 vs. 0.57 SDS, -0.30 to 1.05; p = .67) between individuals with or without a cardiac diagnosis. In the TS population, 55% (31/56) had at least one BP recording above the hypertension threshold. Conclusions Our findings indicate that standardised longitudinal routine monitoring of BP in girls with TS already in childhood is of utmost importance.