The present invention relates to a method and device for determining a relative velocity between a host (100) and a target (102). The present invention relates in particular to a method of the type that can be used in motor vehicle radar systems and specifically in radar systems of the type that detect obstacles in a blind spot of a motor vehicle. In the method according to the invention the following steps are carried out: substantially simultaneously determining a value for a radial velocity and a bearing with regard to a predefined spatial direction for a large number of measurement points (106) on the target (102); calculating a large number of quotients from the radial velocity and the cosine of the associated bearing, a quotient being calculated for each of the measurement points (106); determining an estimated relative velocity between the host (100) and the target (102) by forming an average of the large number of quotients.