Due to its flexibility and ease of patterning, ink jet printing has become a popular technique for the noncontact deposition of liquids, solutions, and melts on a variety of substrates at lateral resolutions down to 10 μm. This article presents a study of ink jet printing of homogeneous layers of Orgacon™ (Agfa-Gevaert, Belgium), a water-based dispersion of poly(3,4-ethylenedioxythiophene):poly (styrenesulfonic acid) (PEDOT:PSS). The printed PEDOT:PSS layer can be used as a transparent electrode in organic light-emitting diodes (OLEDs). Fundamental aspects of the interaction between the ink jet ink and the substrate and the resulting homogeneity of the active layer in relation to OLED device performance are investigated. The optimized PEDOT:PSS ink formulation is shown to improve layer homogeneity, resulting in a uniform light output and device efficiency. Ink jet printing is shown to be capable of fabricating 25×25 mm OLED devices that have equivalent efficiency and light uniformity to the ones produced by spin coating.