A light module for an exterior rearview mirror assembly adapted for attachment to the side of a vehicle comprises an enclosure and a light-transmitting cover. A first light source in the enclosure radiates light through the light-transmitting cover when the light source is electrically powered. A first structure is preferably provided that is configured to mate with a second structure of the exterior mirror assembly in order to at least partially retain the light module substantially within the exterior mirror assembly. The enclosure can be received through an opening in the exterior mirror assembly and the light module may be releasably retained by the first and second structures.