STUDY DESIGN: A two-group experimental design with repeated measures on one factor was used. OBJECTIVES: To investigate the role of the muscle spindles of the paraspinal muscles in lumbosacral position sense of healthy individuals. SUMMARY OF BACKGROUND DATA: Muscle spindles are recognized to be important mediators for position and movement sense in peripheral joints, and they are very sensitive to mechanical vibration. However, little is known about their role in the control of lumbosacral spine positioning. METHODS: Twenty-five young individuals with no low back pain were assigned at random to an experimental or control group. Proprioceptive information of the multifidus muscle spindles was distorted in half of the trials in 16 individuals by manually applying vibration (70 Hz, 0.5 mm amplitude) for approximately 5 seconds. The control group (n = 9) only heard the vibrator noise during repositioning of the lumbosacral spine. Repositioning accuracy in the sitting position was estimated by calculating the mean absolute error, constant error, and variable error among six criteria and reproduction sacral tilt angles. RESULTS: Multifidus muscle vibration induced a significant muscle lengthening illusion through which the members of the experimental group undershot the target position (F(1,15) = 30.77, P < 0.0001). The position sense scores of the control group displayed no significant differences across trials (F(1,8) = 0.56, P > 0.05). CONCLUSIONS: The findings suggest that precise muscle spindle input of the paraspinal muscles is essential for accurate positioning of the pelvis and lumbosacral spine in a sitting posture.