An agitator ball mill including an in particular horizontal grinding container, which has a first end area having a grinding material inlet and a second end area having a grinding material outlet, and a method for operating an agitator ball mill. The agitator ball mill includes a shaft, which can be rotated in the grinding container or in the grinding chamber, respectively, by means of a drive unit and which is formed as agitator shaft at least in sections and which is equipped with agitator elements, as well as a separating device. The separating device includes a classifier rotor, which is arranged on the agitator shaft axially spaced apart from the grinding material outlet and has a rotatable rotor cage, as well as a screen unit, which is arranged within the rotor cage and which is fastened to the classifier rotor.