Optical gain measurements have been performed on several of the lower order modes of a multimode polyimide planar waveguide doped with the laser dye cresyl violet 670. A transverse pumping geometry was employed, resulting in larger gain for higher order modes. In a 21‐mm‐long device, an amplification of 14.4 dB was achieved for the sixth order guided mode at a wavelength of 670 nm. The photostability performance of the waveguide is comparable to the results reported for rhodamine‐doped organically modified silica gels. ©1996 American Institute of Physics.