Measurements of weight, height, mid-upper arm circumference, mid-upper arm muscle circumference and skinfold thickness over the triceps region were made in 437 high-altitude residents (3150m above sea level) aged 16-60 years and 468 low-altitude residents (500 m above sea level) aged 16-60 years in southern Saudi Arabia. Compared with low-altitude residents, high-altitude residents were found to be significantly heavier and taller, but to have nearly similar mid-upper arm circumference, mid-upper arm muscle circumference and triceps skinfold thickness. Estimates of body fat have been made from the triceps skinfold measurements. No significant difference in the percentage of fat was detected between high- and low-altitude residents. When fat mass (kg) and fat mass index (fat mass (kg)/height in m2) were considered, similar trends were found between highland and lowland men only. Highland women showed significantly higher fat mass and fat mass index when compared with lowland women. These differences in physique between highland and lowland residents of southern Saudi Arabia may be attributed to the effect of environmental factors, possibly the hot climate and parasitic infections prevalent in lowland areas, in addition to the higher physical activity observed in lowland women.