We present a valence effective Hamiltonian (VEH) electronic structure calculation on the polyimide poly[N,N′-bis(phenoxyphenyl)-pyromellitimide] , also called PMDA (pyromellitic dianhydride)-ODA (oxydianiline). The most important result is that the valence electronic bands are calculated to be very narrow, even though the calculation is performed on a perfectly stereoregular chain. For instance, the highest 35 occupied valence bands (i.e., the electronic bands with binding energies lower than 18 eV) have widths smaller than 0.25 eV. That result implies that even small disorder effects will tend to strongly localize the electronic processes in polyimide. From the band structure, we calculate the density of valence states and produce a theoretical simulation of the UPS spectrum. Good agreement with the recently published UPS experimental spectrum is obtained. © 1986 American Institute of Physics.