This paper presents the first ab initio attempt to reconstruct the observed band profile of the stretching fundamental vFX (X=H,D) in the FX⋅⋅⋅O(CH3)2 hydrogen‐bonded system. The two‐dimensional potential energy surface V(rFH,RF⋅⋅⋅O) is evaluated by means of large basis set SCF calculations. The related force constants up to the fourth order are obtained via the analytical fit to a polynomial expansion. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical anharmonicity. The side bands of the stretching fundamental vFX are described in terms of the vFX ±nvFX⋅⋅⋅O combination bands in excellent agreement with experiment.