There is evidence that increased bladder wall thickness can be a useful parameter in the evaluation of men with clinical benign prostatic hyperplasia (BPH). However, normal values for bladder wall thickness (BWT) in adults have not been established. BWT was measured by suprapubic ultrasonography. Bladder volume was calculated as the product of the ultrasonographic measurements of bladder height, width and depth, and a correction factor (0.6). Three groups were assessed: men with normal lower urinary tracts (n = 172; mean age, 39.9), women with normal lower urinary tracts (n = 166; mean age, 37.8), and men with mild lower urinary tract symptoms (LUTS) and clinical benign prostatic enlargement (BPE) (n = 150; mean age, 66.4). For the whole group of men and women with normal bladders, mean BWT was 3.35 mm, and BWT appeared normally distributed. There were a weak negative correlation with bladder volume (r = -0.12, P < 0.003) and a weak positive correlation for BWT and age for both men (r = 0.12, P < 0.014) and women (r = 0.17, P < 0.013). Mean BWT was 3.04 mm in healthy women, 3.33 mm in healthy men, and 3.67 mm in men with LUTS and BPE. Sub-dividing normal men into different age groups showed an increasing mean BWT of 3.08 mm (<20 years, n = 27), 3.25 mm (21-40 years, n = 75), 3.42 mm (41-60 years, n = 39), and 3.57 mm (>60 years, n = 31) for those sub-groups. BWT in normal adult women is 3.0 +/- 1 mm and 3.3 +/- 1. 1 mm in normal adult men. A small increase in BWT with age is seen for both genders, and BWT tends to be greater in men than in women. Men with LUTS and BPE show a moderate increase in BWT. Adjustments for bladder volume are for practical purposes negligible, although there is a small decrease in BWT with increasing volume.