Twenty four hour BP is more representative of the true BP profile of a person. The BP variation throughout the day is known to be related to cardiovascular outcomes. Non-dipping BP pattern is associated with poor prognosis in left ventricular function. Early morning BP rise/surge has been linked with ischemic stroke. The effect of 24 hour BP pattern on the LV structure and function has not been examined in newly diagnosed hypertensive Nigerian. OBJECTIVES To assess the 24 hour BP pattern and its relationship with the LV structure and function in newly diagnosed hypertensives in Nigeria. METHOD Twenty four hour BP monitoring was performed on 210 hypertensives and 202 controls. Three (3) casual BP measurements were taken when the subjects were rested using standardized digital BP machine. Mean of the 3 measurements was used to categorize the subjects as hypertensives or normotensives (controls). Schiller BR-102 ABPM machine which had been calibrated was used to measure the 24 hour BP. Daytime and night time systolic and diastolic blood pressures were acquired every 20 minutes. Ten percent decrease in BP between daytime and night time was used to categorize the subjects as dippers or non-dippers. Similarly a 10% increase in BP on waking in the morning differentiated the risers from non-risers. Echocardiography was performed on 105 subjects and 95 normotensive controls using ALOKA SSD-1,700 according to the American Society of Echocardiography (ASE) criteria. LVM was indexed by the allometric power of height (height2.7) and LVH was considered present if left ventricular mass index (LVMI) is equal to or greater than 49.2g/m2.7 in males and 46.7g/m2.7 in females as documented by Adebiyi et al among Nigerians. RESULTS The hypertensives and the controls were comparable in the demographic characteristics. More hypertensive added salt in their meals on table compared to normotensives, 63.8% versus 29.2%. Cut off limits for normal ABP used in the study were 125/80mmHg for 24-hour blood pressure, 135/85mmHg and 120/70mmHg, for awake and asleep blood pressures respectively. Among hypertensives, mean casual BP and mean 24 hour BP were 165.10(15.6)/95.5(8.0) mmHg and 131.72(22.55)/83.59(14.88) mmHg respectively (p<0.0001). Among the normotensives, the values were 127.7(11.20)/75.6(8.70) mmHg and 111.84(13.05)/69.91(10.0) mmHg (p< 0.0001). In all the groups and sub-groups studied casual BP was remarkably higher than the mean 24 hour BP. Sixteen percent of the hypertensives and 60% of the normotensives had normal LV geometry and concentric hypertrophy was found in 41.9% of the hypertensive population. Hypertensive non-dippers constituted 71.4% of this group and were older. About 49.5% of the normotensives were non-dippers. LVMI and aortic root size were higher in hypertensive non-dippers than for the dippers, 51.82(12.01) vs 46.58(9.85) g/m2.7 p=0.018 and 3.02(0.33)cm vs 2.86(0.24)cm p=0.013 respectively. Normotensive non-dippers also had higher LVMI than the dippers, 36.21(9.25) versus 34.80(7.97)g/m2.7 though this was not statistically significant.(p=0.50). Hypertensive non-risers made up 60% of this group, and they were older, 49.05(11.62) vs 43.75(12.56) p=0.002. LVMI of hypertensive non-risers was 52.9g/m2.7 vs 46.4g/m2.7 for risers, p<0.001. The SBP of nondipping and non-rising BP subgroups correlated with LVMI whereas the DBP of the dipping and the rising subgroups correlated with LVMI. The LV functions were all normal and showed no statistically significant difference in the various groups and sub-groups. Gender differences between the groups and sub-groups were equivocal. CONCLUSION 24-hour blood pressure variation is associated with significant cardiovascular consequences in our population. Majority of our hypertensives are non-dippers and non-risers. Non-dipping and non-rising blood pressure pattern are independent risk factors for increased left ventricular mass. In same vein, concentric hypertrophy which portends poor left ventricular state is more common in non-dippers and non-risers. This study did not show early morning blood pressure surge as being very prominent in our hypertensive population. Non-dipping and non-rising BP had correlation with SBP and LVMI, whereas dipping and rising BP showed correlation between DBP and LVMI