Window chambers are support structures implanted in the dorsal skin fold of a rodent model. Optical imaging of window chambers has been used in many basic cancer and vascular biology studies. We have recently shown that this technique can be extended to MRI by using plastic rather than metal window chambers. Here we describe a system for simultaneous optical and MR imaging of the window chambers. It provides many possibilities for independent cross validation of the measurements of one modality from the other. In the system, a GRIN lens images the tissue to the distal end of a coherent imaging fiber bundle, which relays this image to a camera system located outside the magnet room. Both trans- and epi-illumination are provided to this system. Light sources are located outside the magnet room and the light is delivered through fiber optics. A group of fibers are used to deliver white light from under the window chamber for standard transmission imaging, while another single fiber delivers the laser light from the top to induce fluorescence. An appropriate bandpass emission filter is inserted between the lenses at the camera end for fluorescence imaging. Results of simultaneously optical and MR imaging of tumor and vessel are presented.