Method for controlling emissions of nitrogen oxides at the outlet of the exhaust box of a motor vehicle fitted with an internal-combustion engine associated with at least one post-treatment system (16, 17) for the nitrogen oxides emitted in the combustion gases of the engine, including at least one stage for determining the mean quantity of nitrogen oxides per travelled kilometer (FC lt) emitted by the vehicle from the start of a journey to the time the vehicle is stopped, CHARACTERIZED IN THAT it includes, iteratively at each step of the fixed elementary distance (ΔD) travelled, from the beginning of the journey and until the vehicle is stopped: - a stage in which a short-term conformity factor (FC st) that is equal to the mean quantity of nitrogen oxides per travelled kilometer emitted over said elementary distance (ΔD) that has just been travelled, and a long-term conformity factor (FC lt) equal to the mean quantity of nitrogen oxides per travelled kilometer over the distance travelled from the start of the journey are determined, - a stage in which said long-term conformity factor (FC lt) is compared to a threshold (FC, FC'), and - a stage in which, when said long-term conformity factor (FC lt) is greater than said threshold (FC, FC'): i. a set of parameters representative of the operating point of the engine is determined, including at least the torque of the engine, the speed of the engine and the water temperature (T eau) of the engine, and ii. the engine and/or the post-treatment system (16, 17) are set, corresponding to a concentration of nitrogen oxides [NO x] tp at the outlet of the exhaust box of the vehicle that ensures that the short-term conformity factor (FC st) determined in the following step is strictly below said threshold (FC, FC'). - a stage in which a short-term conformity factor (FC st) that is equal to the mean quantity of nitrogen oxides per travelled kilometer emitted over said elementary distance (ΔD) that has just been travelled, and a long-term conformity factor (FC lt) equal to the mean quantity of nitrogen oxides per travelled kilometer over the distance travelled from the start of the journey are determined, - a stage in which said long-term conformity factor (FC lt) is compared to a threshold (FC, FC'), and - a stage in which, when said long-term conformity factor (FC lt) is greater than said threshold (FC, FC'): i. a set of parameters representative of the operating point of the engine is determined, including at least the torque of the engine, the speed of the engine and the water temperature (T eau) of the engine, and ii. the engine and/or the post-treatment system (16, 17) are set, corresponding to a concentration of nitrogen oxides [NO x] tp at the outlet of the exhaust box of the vehicle that ensures that the short-term conformity factor (FC st) determined in the following step is strictly below said threshold (FC, FC'). i. a set of parameters representative of the operating point of the engine is determined, including at least the torque of the engine, the speed of the engine and the water temperature (T eau) of the engine, and ii. the engine and/or the post-treatment system (16, 17) are set, corresponding to a concentration of nitrogen oxides [NO x] tp at the outlet of the exhaust box of the vehicle that ensures that the short-term conformity factor (FC st) determined in the following step is strictly below said threshold (FC, FC').