Background: Paediatric primary hypertension is partly attributable to the childhood obesity epidemic. 24-hour ambulatory blood pressure monitoring could better identify blood pressure alterations in this group. The aim of the present study is to estimate the proportion of blood pressure abnormalities in obese children and the prevalence of the different blood pressure categories according to the American Heart Association. Procedure: A case-control study was designed (n=154, 53.2%boys) including 77 obese and 77 normal-weight children aged 7-15 years. International Obesity Task Force reference values were used to define obesity and normal weight. Office blood pressure and ambulatory blood pressure for 24h were assessed and children were classified according to the American Heart Association categories. Results: Means of systolic and diastolic blood pressure were higher in obese participants. Office’s systolic hypertension was present in 19.5% of obese vs 5.2% of normal-weight and night-time systolic hypertension affected 11.7% of obese vs 2.6% of normal-weight (p <0.05). Non-dipping was present in 54.5% of obese vs 35.1% of normal-weight in the systolic register (p=0.015). Prevalence of abnormal blood pressure loads was higher in obese. Exclusively in the night-time, ambulatory hypertension was diagnosed in obese children (3.9%). A high proportion of obese were uncategorized. Conclusions: A high proportion of blood pressure abnormalities has been observed taking into consideration the entire 24h, daytime and night-time periods. Only with the office BP reading, the primary hypertension seems to be over-diagnosed. There is still an urgent need for more comprehensive studies linking ambulatory blood pressure patterns to cardiovascular event