Using a variable temperature STM, we have observed the adsorption of DMSO on Au(100) and Au(111) surfaces at temperatures below 215 K. For DMSO on Au(100), the molecules are trapped on the terraces at high points on the hex reconstruction giving rise to an ordered low coverage phase. Consistent with data from previous temperature programmed desorption (TPD) measurements, this phase coexists with a higher coverage "striped" phase formed when the DMSO molecules associate with each other. On Au(111), the DMSO molecules nucleate, order, and grow only from step edges; the steps are the only appropriately electropositive sites on this surface.