Background: The aim of this study was to evaluate in non-hypertensive children following renal transplantation (TX) the rates and determinants of transition to hypertension. Methods: Retrospective case note review of all current paediatric kidney transplant patients in the UK. At baseline (6 months following TX), all included subjects were non-hypertensive with systolic and/or diastolic clinic blood pressure (BP) 95th percentile while on no anti-hypertensive therapy. We assessed progression from optimal (systolic and/or diastolic clinic BP 50th percentile), normal (systolic and/or diastolic clinic BP epsilon 50th but 90th percentile) and pre-hypertension (systolic and/or diastolic clinic BP 90th95th percentile) to hypertension (systolic and/or diastolic clinic BP 95th percentile). If systolic and diastolic BP levels belonged to different categories, the higher of the two levels were used for categorization. Results: At baseline, 146 of 524 (27.9%) children (106 male) median [inter-quartile range (IQR)] age 7.8 years (4.8, 11.8) were non-hypertensive and not on any anti-hypertensive therapy; there were 34 patients (23.2%) with optimal BP, 90 (61.6%) with normal BP and 22 (15.1%) with pre-hypertension. They were followed up for a median of 2.0 (1.0, 4.0) years post-TX. At the end of follow-up, BP was optimal in 37 patients (25.3%), normal in 35 (24.0%), high normal in 2 (1.4%) and 72 (49.3%) had progressed to hypertension. The KaplanMeier estimated time at which 50% of patients developed hypertension was 2.0 years for the pre-hypertension and 3.0 years in the normal BP group as opposed to 40% risk at 7-year post-TX in the optimal group (P 0.001 between the three groups). The differences between BP groups remained significant after adjustment for all risk factors on multivariate analysis. Conclusions: Just over 49% of our initially non-hypertensive patients progressed to hypertension following TX. BP needs careful monitoring post-TX and ideally should be maintained in the onormal' and ooptimal' range.