Poly(3,4 ethylene dioxythiophene)/ poly(styrene sulfonate) (PEDT/PSS) blends are widely used in organic light-emitting diodes (OLEDs) to enhance their performance. Using neutron reflectometry to study such blends, it is shown that substantial segregation of the blend components occurs at the surface (see Figure), a result that will have implications both for the performance and for the stability of optoelectronic devices using PEDT/PSS.