A parking aid system for a vehicle includes a device that measures the instantaneous distance of a vehicle part from an obstacle located in its path and generates at least one output signal indicative of the measured distance, as well as a device capable of issuing warning signals. An evaluating unit is connected between the measuring device and the warning device. The evaluating device dynamically determines, as a function of vehicle speed, an instantaneous distance limit value, compares the measured distance value with the respective distance limit value and activates the warning device when the measured distance value is smaller than the respective distance limit value to alert the driver of the vehicle to the presence of the obstacle. The distance limit value may be determined by adding a first distance value independent of the speed of the vehicle and a second distance value linearly proportional to the speed of movement of the vehicle. The proportionality constant for the second distance value is at least equal to at least one of the reaction time of the driver, the reaction time of the measuring means, the dead time of the braking system of the vehicle and the time that is required to stop the vehicle after the braking system has become effective.