We report on the imaging of single dye molecules in thin polymer films under ambient conditions by means of scanning near-field optical microscopy. The long-term mechanical stability and high detection efficiency of our instrument allow the imaging of single dye molecules over several hours with a high signal-to-noise ratio. The local excitation by the near-field tip, the low excitation power and the fact that the dye molecules are embedded in the three dimensional polymer structure drastically reduce photodestruction as compared with conventional microscopy. The observation of many molecules in the same film allows to probe them under identical experimental conditions and to statistically analyze their global behavior. We find that the molecules diffuse and rotate within the polymer matrix. The single dye molecules act as nanometer-sized probes and reflect the local structure of the polymer.