It is well recognized that serum creatinine level provides a quick general assessment of renal function. However, we frequently encounter elderly hypertensive patients with renal involvement whose serum creatinine levels are within normal limits. The aim of this study was thus to determine whether serum creatinine level is a sensitive indicator of renal function in elderly hypertensive patients. Study groups were classified according to age: 82 elderly patients (aged 65 yr or older) and 98 middle-aged patients (aged 40-65 yr) with essential hypertension. To assess hypertensive renal involvement, serum creatinine and serum uric acid levels were measured. We also measured the left ventricular mass (LVM) index by using echocardiography as a marker of hypertensive target organ damage. There was no age-related difference in the LVM index, but the serum creatinine level in elderly hypertensive patients was significantly lower than that in middle-aged hypertensive patients. There was no significant difference in serum uric acid level between the two groups. In addition, the LVM index was correlated with the serum uric acid level (r = 0.46, p = 0.0001) but not with the serum creatinine level in elderly hypertensive patients. In middle-aged hypertensive patients, the LVM index was related to both serum uric acid level (r = 0.41, p = 0.007) and serum creatinine level (r = 0.43, p = 0.003). In conclusion, serum creatinine level may underestimate hypertensive renal involvement in elderly hypertensive patients. In contrast, serum uric acid level may be a sensitive indicator of hypertensive target organ damage irrespective of age.