Porphyrins are used industrially for LCD displays, catalysts, sensors and for solar energy conversion due to their characteristic photophysical properties, and have potential application in molecular electronic devices. Understanding the self-organization and assembly of porphyrins on various surfaces is vital to optimization of these devices. There are a wide range of experimental conditions (solvents, concentrations) reported for studies of the morphology and organization of porphyrins on surfaces. Typically, planar porphyrins attach to surfaces in a co-planar configuration. Strong pi-pi interactions between the macrocycles often result in columnar discotic phases (stacks), analogous to a stack of coins. Using scanning probe microscopy (SPM), we are investigating the self-assembly of 5,10-diphenyl-15,20-di-pyridin-4-yl-porphyrin on highly ordered pyrolytic graphite (HOPG). Our studies show that samples prepared by drop-cast methods or immersion of various substrates in porphyrin solutions spontaneously produce “stacks” when dried naturally, for a range of concentrations and solvents. Ambient SPM images of the nanostructures formed under these conditions reveal that the lateral and vertical dimensions of the porphyrin stacks are astonishingly uniform, and aggregation of stacks is not observed, even at much higher concentrations. Possibly, the natural drying step spontaneously leads to stacking in solution; as the solvents evaporate, the macrocycles are physically pulled together into organized columnar stacks. To test this hypothesis, we prepared a sample using evaporative drying at 10-6 Torr. Images using AFM reveal a continuous film without stacks forms on HOPG when using evaporative drying. The film thickness corresponds to a single layer of porphyrins adopting a co-planar orientation.