An organic light emitting diode (OLED) uses a π-conjugated polymer emissive layer (MEH-PPV) sandwiched between two semitransparent electrodes. The preferred embodiment utilizes an optically thin gold film anode, whereas the cathode was in the form of an optically thick aluminum (Al) film with patterned periodic subwavelength 2D hole array that showed anomalous transmission in the spectral range of the polymer photoluminescence band. At similar current densities we obtained a seven-fold electroluminescence efficiency enhancement with the patterned Al device compared with a control device based on unperforated Al electrode.