Objective To investigate the characteristics of ambulatory blood pressure levels and circadian rhythm in the youth with essential hypertension(EH) before and after treatment.Methods 95 young patients with EH were treated with antihypertensive drugs.Four indexes of 24-hour ambulatory blood pressure monitor were measured and compared before and after treatment,including mean blood pressure,mean pulse pressure,blood pressure load and blood pressure circadian rhythm.Results Systolic pressure and diastolic pressure in EH patients were all higher than the normal value in the whole day but decreased obviously(P 0.05) after the treatment.Before the treatment,the systolic pressure load was 30%and the diastolic pressure load was 36%in daytime;which was 28%and 32%at night.After the treatment,the systolic pressure load decreased to 4%in daytime and 3%at night;the diastolic pressure load decreased to 3%in daytime and 4%at night.The differences were statistically significant(P 0.01).The patients with abnormity in circadian rhythm of blood pressure(nondipper) account for 81.1%(77/95 ) before the treatment.The decrease rates of systolic pressure and diastolic pressure during the night were all increased obviously(P 0.05) after the treatment.However,there was only 19.5%(15/77) nondipper blood pressure circadian rhythms changing into dippers.Conclusion After treatments young EH patients had much lower mean blood pressure and blood pressure load in the whole day.Decrease rate of blood pressure during the night increased obviously,whereas only a part of patients recovered to normal blood pressure circadian rhythms.