The kinematic analysis system ZEBRIS CMS-HS allows to calculate, in real time, the 3D coordinates of kinematic markers using the principle of ultrasonic triangulation. However ultrasounds propagation may be altered by external factors. Several disruptive conditions (reflection of ultrasonic waves, wind, temperature variations, shifting of the transmitters relative to the microphones) have been tested. The 3D coordinates of six immobile markers have been measured and theoretically invariable angles and distances have been calculated. The precision was evaluated according to the standard deviation of each series. In standard laboratory conditions, the precision was ± 0.14 mm for distances and ± 0.16° for angles. Ultrasound reflections can induce systematic errors (about 0.2°) and impair the repeatability of the measures. Wind decreases the precision of the measures in proportion to its speed. Configuring temperature in the software is necessary because it conditions the accuracy of the measures. A decrease of the precision was also observed when the transmitters were moved away from the microphones, at a distance higher than 1.5 m. This study provides a better knowledge of the causes of alteration of the measures and allows to determine the limitations of the system.