This method for determining an obstacle avoidance guidance law for an aircraft is implemented by a system for determining said guidance law. The aircraft comprises a collision avoidance system adapted to detect a collision risk with the obstacle and said determination system. This method comprises determining one or more set points from among flight path angle and speed set points, at least one set point depending on at least one vertical speed limit value, at least one set point comprising a vertical component in a vertical direction, each limit value being provided by the collision avoidance system following the detection of a collision risk with the obstacle; and computing the avoidance guidance law as a function of the determined set points. During the determination step, at least one determined set point comprises a longitudinal component in a longitudinal direction perpendicular to the vertical direction.