Ab initio calculations were carried out on the tGg, tGt, and gGg conformers of 1,2-ethanediol in the gas phase and then Monte Carlo simulations were carried out in aqueous solution. MP2/6-31G*//6-31G* results with zero-point and thermal corrections (T=298 K) show that these conformers without intramolecular hydrogen bonding are higher in free energy by 3-4 kcal/mol than the most stable tGg' conformer. Hydration of the tGg conformer leads to stabilization by 5.2 kcal and is the most likely conformer in aqueous solution. It represents 64% of the conformer population considering in aqueous solution