OBJECTIVE: To determine the prevalence of both systolic and diastolic hypertensions in relation to age and their impacts on target organ among adult Nigerians with hypertension. DESIGN: Observational study. PLACE AND DURATION OF STUDY: The Cardiovascular Clinic of the University of Ilorin Teaching Hospital, Nigeria, from July 2002 to June 2003. PATIENTS AND METHODS: Newly diagnosed adult hypertensives, with blood pressure >or= 140/90mmHg, taken twice with mercury column sphygmomanometer at 3 weeks interval, were studied. The total number of hypertensive patients treated over this period was also taken into consideration. The newly diagnosed hypertensives were classified using JNC VI classification. The frequency of occurrence of target organ damage such as Left Ventricular Hypertrophy (LVH), heart failure, renal impairment etc. was charted according to systolic and or diastolic pressures. The occurrence of systolic or diastolic blood pressure was also related with the age of the patients. Blood metabolic parameters were compared in both systolic and diastolic blood pressures for their possible contributory role. RESULTS: Two thousand seven hundred and ninety-two adult hypertensive patients were managed over the study period. Of them, 218 (7.8%) were newly diagnosed and studied. There were 94 males and 124 females. Seventy-seven (35.3%) were aged 60 years and above with equal frequency in the gender. One hundred and seventy-eight (81.7%) cases had combined systolic and diastolic pressures. Twenty-nine (13.3%) patients had systolic hypertension. Twenty-five (86.2%) of these 29 were aged 50 years and above and 20 (69.0%) were aged 60 years and above. Eleven (5.0%) patients had isolated diastolic hypertension and they were all in the age bracket 40-49 years. Systolic blood pressure was found to be rising with advancing age while diastolic blood pressure peaked at mid 40's and declined. Target organ damage occurred more frequently with systolic hypertension and advancing age than with diastolic hypertension. CONCLUSION: Systolic hypertension occurred more frequently in this series of adult Nigerians with hypertension. It was higher with advancing age and associated with more target organ damage than the diastolic hypertension.