Case reports show hypertension in children treated with GnRH analogues for central precocious puberty (CPP). However, relevant data on blood pressure are scarce. We aimed to evaluate blood pressure (BP) among girls with idiopathic CPP and early-onset puberty before and during GnRH analogue therapy; and to examine associations of blood pressure with clinical parameters. For this retrospective longitudinal cohort study, demographic, anthropometric, clinical, and laboratory data were collected from electronic files. The study group included 112 girls with idiopathic CPP or early-onset puberty followed in a tertiary pediatric endocrinology institute, and a control group of 37 healthy pre-pubertal girls. The main outcome measures were BP percentile, before, and during treatment with GnRH analogue. At baseline, similar proportions of the study and control groups had BP values>90th percentile: 64 (53 %) and 17 (46 %), respectively (p=0.57). The mean systolic and diastolic BP percentiles measured under treatment remained unchanged. In the study group, baseline BP>90th percentile compared to normal baseline BP was associated with lower birthweight and a higher body mass index-standard deviation score: 2,821 ± 622 vs. 3,108 ± 485 g and 1.0 ± 0.7 vs. 0.70 ± 0.8, respectively, p=0.01 for both. GnRH analogue therapy for precocious or early puberty was not associated with increased blood pressure. The stability of mean blood pressure percentile during treatment is reassuring.