Falls lead to significant morbidity and mortality in persons older than 65 years of age. Impaired proprioception may be a contributing factor to falls, and this may be influenced by the level of habitual physical activity. The primary purpose of this study was to investigate knee joint proprioception among young volunteers and active and sedentary elderly volunteers. Knee joint proprioception was measured through reproduction of static knee angles using a Penny and Giles electrogoniometer. The secondary purpose of this investigation was to test the reproducibility of the Penny and Giles electrogoniometer in measuring static knee angles. Sixteen young subjects (age range, 19-27 years) and 24 elderly subjects (age range, 60-86 years) participated. Subjects were given a screening history and physical examination to exclude neuromuscular or vestibular disorders or lower limb injuries. Knee joint proprioception was measured two times during one week. The elderly group was separated into active and sedentary subgroups based on their level of activity during the past year. The electrogoniometer was placed laterally across the dominant knee joint. From the prone position each subject attained one of ten randomly predetermined knee joint angles from 10 degrees to 60 degrees. The subject then returned to the starting position and reproduced the test angle. The absolute angular error (the absolute difference between the test angle and subject perceived angle of knee flexion) was determined. A positive correlation was found between control visits for all subjects (r = 0.88), and significant differences were observed between young (mean, 2.01 +/- 0.46 degrees) and active-fold (mean, 3.12 +/- 1.12 degrees; P < 0.001), young and sedentary-old (mean, 4.58 +/- 1.93 degrees; P < 0.001), and active-old and sedentary-old (P < 0.03). These findings demonstrate that the Penny and Giles electrogoniometer is a reproducible device for measuring knee joint angles in both young and elderly subjects. Furthermore, we found that proprioception is diminished with age and that regular activity may attenuate this decline. One strategy to reduce the incidence of poor proprioception and fall with ageing may be regular exercise.