The invention concerns a device for uphill start-up assistance for a motor vehicle. The invention is characterised in that the assistance device (15) comprises means (9) for controlling the release of the vehicle mechanical brakes (5) which act on the vehicle wheels (4), so that the vehicle is maintained in the slope when manoeuvring uphill without any intervention from the driver on this maintaining condition. The means (9) uses mainly the state of the slope indicated by a means (7), the interpretation and anticipation of the commands of driver and/or of a central driving member (14) by a means (7) and the instantaneous clutching characteristics (2) determined by a means (8). In a preferred embodiment, the assistance device co-operates with an electrical device of the parking brake.