A medication delivery device comprising: a device body; a dose setting member attached to said device body and rotatable relative to said device body about an axis of rotation during dose setting and during dose delivery; a sensed element rotationally fixed with said dose setting member, said sensed element attached to or formed integrally with said dose-setting member, said sensed element including alternating first and second surface features (100, 102) radially-spaced about the axis of rotation of said dose setting member; an actuator attached to said device body, said actuator being axially and rotationally fixed with said dose setting member in a first operating mode during dose setting, said actuator being movable axially distally but non-rotatably relative to said device body in a second operating mode during dose delivery, said sensed element and said dose setting member rotating relative to said actuator during dose delivery in relation to the amount of dose delivered; and a rotation sensor attached to said actuator during dose delivery, said rotation sensor including a light source emitting sensing light in a sensing direction during dose delivery, said rotation sensor further including a light sensor positioned to receive the sensing light emitted in the sensing direction during dose delivery, wherein in the first operating mode the alternating first and second surface features are axially displaced from the light source and the light sensor, and wherein the rotation sensor is movable axially distally relative to the sensed element by axial distal movement of the actuator relative to the device body in the second operating mode such that the alternating first and second surface features become received between the light source and the light sensor, rotation of said sensed element during dose delivery positioning the first and second surface features in the path of the sensing light, the first surface features resulting in the sensing light being detected by the light sensor, the second surface features resulting in the sensing light not being detected by the light sensor, the rotation sensor being responsive to the detection or non-detection of the sensing light to detect rotation of said dose setting member relative to said actuator during dose delivery; and an electronics assembly responsive to the rotation sensor to determine the amount of dose delivery based on the detected rotation of said dose setting member relative to said actuator during dose delivery. a device body; a dose setting member attached to said device body and rotatable relative to said device body about an axis of rotation during dose setting and during dose delivery; a sensed element rotationally fixed with said dose setting member, said sensed element attached to or formed integrally with said dose-setting member, said sensed element including alternating first and second surface features (100, 102) radially-spaced about the axis of rotation of said dose setting member; an actuator attached to said device body, said actuator being axially and rotationally fixed with said dose setting member in a first operating mode during dose setting, said actuator being movable axially distally but non-rotatably relative to said device body in a second operating mode during dose delivery, said sensed element and said dose setting member rotating relative to said actuator during dose delivery in relation to the amount of dose delivered; and a rotation sensor attached to said actuator during dose delivery, said rotation sensor including a light source emitting sensing light in a sensing direction during dose delivery, said rotation sensor further including a light sensor positioned to receive the sensing light emitted in the sensing direction during dose delivery, wherein in the first operating mode the alternating first and second surface features are axially displaced from the light source and the light sensor, and wherein the rotation sensor is movable axially distally relative to the sensed element by axial distal movement of the actuator relative to the device body in the second operating mode such that the alternating first and second surface features become received between the light source and the light sensor, rotation of said sensed element during dose delivery positioning the first and second surface features in the path of the sensing light, the first surface features resulting in the sensing light being detected by the light sensor, the second surface features resulting in the sensing light not being detected by the light sensor, the rotation sensor being responsive to the detection or non-detection of the sensing light to detect rotation of said dose setting member relative to said actuator during dose delivery; and an electronics assembly responsive to the rotation sensor to determine the amount of dose delivery based on the detected rotation of said dose setting member relative to said actuator during dose delivery.