We demonstrate a purely solvent-based approach to assembling CdSe nanorods into vertically aligned, hexagonally packed monolayers in solution. Nanorods were dispersed in a mixture of good solvent with high vapor pressure and bad solvent with low vapor pressure, and preferential evaporation of the good solvent led to ordered assembly under conditions of continuously decreasing solvent quality. No applied external bias, extensive control of drying conditions, exceptionally monodisperse nanoparticles, or high concentrations of additives were required. This clean and facile method yielded ordered nanorod sheets of up to 7.5 mu m wide with potential use as active materials in unique applications.