Abstract: AIM:To study the clinical manifestations and relative factors of nondipping hypertension in order to improve its diagnosis and treatment. METHODS: Patients with primary hypertensive or other cardiovascular diseases without severe complications were selected. After collecting clinical data including laboratory blood sample analysis, electrocardiograph (ECG) and echocardiogram examination, all patients underwent a 24-h ambulatory blood pressure monitoring (ABPM) procedure. Nocturnal blood pressures (BP) were compared with diurnal BPs. Dipping hypertension was defined if the mean nocturnal reduction of BP was 10% or above, whereas nondipping BP was defined if the reduction was <10%. The anti-dipper BP was defined if there was no drop in nocturnal BP. Clinical manifestations of these types were compared. RESULTS: Among the 55 selected patients diagnosed with class 2 or 3 hypertension, dipping hypertension, nondipping hypertension and anti-dipping hypertension were detected in 19 (35%), 22 (40%) and 14 (25%) cases, respectively. Statistical significance was found among the three groups in aspects such as age, historical episode of coronary disease or stroke, blood serum urea nitrogen (BUN) level, and mean nocturnal systolic/diastolic blood pressure (SBPn/DBPn). Logistic regression analysis indicated that history of coronary diseases or stroke and high BUN level were contributing factors to the abnormal circadian rhythms of BP. CONCLUSION: Morbidity of nondipping hypertension is relatively high in hospitalized patients. Coronary disease, stroke and high level BUN are defined as its relative factors.