An illumination unit for microscopes has an MID structure for the free spatial arrangement of different electronic and optical components, so that surfaces of a three-dimensional carrier are available as a replacement for printed circuit boards. The MID structure designed as an illumination unit contains a closed annular main part having an annular free beam opening, where columns are arranged on the main part. On the free ends of the columns, illumination means are provided which can be contacted via conductor paths provided on the surface of the MID structure. The columns contain a cooling structure on a side surface facing away from the free beam opening, and a plug for the power supply and a control unit for controlling the illumination means are provided on the main part of the MID structure. The MID structure designed as an illumination unit is provided in a housing of a microscope objective.