Nonempirical RHF/STO-3G and 6-31G(d) studies on conformational behavior of tetrahydro-1,3-oxazine showed that interconversion between the axial (global minimum) and equatorial chair conformers can follow five independent pathways. The potential energy surface contains seven minima corresponding to chair and twist conformers, as well as seven transition states having sofa, half-chair, and symmetrical and unsymmetrical boat conformations. Additional potential barriers to interconversion, resulting from pyramidal inversion of the nitrogen atom, were also revealed.