Osteoporotic vertebral fractures result in loss of height and so regular measurement of stature may be a useful method for detecting the onset of the disease and monitoring its progress. The aim of this study was to evaluate the reliability of height measurement in a clinical setting by estimating its precision and the effects of diurnal variation and supine bone densitometry. Duplicate measurements of standing height were made in 50 normal volunteers (25 female) in the morning and 7h later; similar measurements were made in 25 female patients before and after densitometry (spine, one hip and whole body). Portable Harpenden stadiometers were used. The pooled standard deviation (coefficient of variation) ranged from 0.9 mm (0.05%) to 1.7 mm (0.11%). Significant height decrease (> 6 mm) occurred in volunteers during the course of a day while patients showed a significant increase (> 5 mm) after lying supine for an average period of 49 min. Height can be estimated precisely if measurements are made consistently, i.e. using the same equipment and technique, at the same time of day and before bone densitometry. The provision of stadiometers in primary care surgeries and hospital clinics would provide a simple, inexpensive and non-invasive method of assessing the progress of spinal osteoporosis.