An obstacle detection method and system, particularly for car parking systems comprising emitting ultrasound signals at a plurality of sensors, receiving echo signals returned by at least one obstacle, performing a parametric evaluation of the received signals, determining, for each sensor, the distance between the sensor and an obstacle detected by it, associating with each sensor a value of the distance from the obstacle detected by it; determining a value corresponding to the minimum detected distance and replacing it with the sum value between a minimum distance and a priority threshold value; assigning to the sensor that detected the minimum distance a priority status; and defining a sensor polling cycle that polls more frequently a priority status sensor than non-prioritized sensors.