The experimental gas phase specific rotation of (S)-propylene oxide at 355 nm is correctly predicted at the DFT/ B3LYP level of theory only adopting fairly large basis sets, such as aug-cc-pVTZ and aug-cc-pVQZ, or, alternatively, the much smaller polarizability-consistent Sadlej basis set. Therefore, considering also the sensitivity to solvent effects, this small and rigid molecule, which has been considered an ideal test case for theoretical investigations, is, on the contrary, one of the most difficult cases to be treated. (C) 2003 Elsevier B.V. All rights reserved.