Background/Objective: This study assessed the extent to which ulna length could be used to predict height and body mass index (BMI) in various groups of English and Portuguese hospitalised patients, and tidal volumes in critically ill patients at risk of requiring ventilatory support. Subjects/Methods: Bedside measurements of weight, height and ulna length were made in 507 patients (432 English, 75 Portuguese; 264 men, 243 women) with a mean age of 61.8 ± 18.9 years, height 165.1 ± 9.5 cm and BMI 26.7 ± 5.43 kg/m 2 . Results: Ulna length could be measured with ease in all subjects. The intra-observer technical error of measurement in the same subjects was 1%. Within each category of men and women aged o65 years and 65 years and over, there was no significant difference between the English and Portuguese in the intercept or regression coefficients for the ulna-height relationships. A strong relationship was found between predicted and measured height (r ¼ 0.963, standard error of the estimate 4.6 cm). The overall mean and s.d. of the difference was 0.3±2.7% of height, with no significant difference between English and Portuguese populations. The discrepancy between measured and predicted BMI corresponded to 0.7 ± 5.5% (s.d.) (all subjects) and for ventilatory volumes predicted from height (critically ill subjects only) 0.7±7.1%. Conclusion: Height can be predicted from ulna length with precision and ease in a wide range of patient groups, and without the need to use different equations in English and Portuguese populations. The predicted measurements are acceptable in most clinical circumstances.