The potential energy surfaces of five-membered homo- and hetrerocyclic saturated rings (cyclopentane, tetrahydrofuran, tetrahydrothiophene, pyrrolidine and N-methylpyrrolidine) have been studied using molecular mechanics, semiempirical (MNDO, AM1 and PM3) and ab initio methods (HF/6-31G**) to determine the ability of each in describing the geometry and stability of each of the mentioned compounds. The molecular mechanics and ab initio calculations are consistent in the realative energies and geometries determined for the conformers of all ring systems, whereas the semiempirical calculations yield flatter geometries and scattered energies. The PM3 method produces the best results among the semiempirical methods tested.