The molecular geometry of a major metabolite, C14H19NOS, of a potent anti-arrhythmic drug, 7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane (BRB-I-28), has been determined by X-ray diffraction. The 3,7-dihetero bicyclic system of the sulfoxide molecule adopts a chair--chair conformation like that of the HCLO4 salt of the BRB-I-28 molecule. The S...N contact distance of 2.863(2)A in the present molecule is significantly shorter than that found in the crystal structure of its precursor [3.038(4)A]. The overall molecule possesses pseudo-mirror symmetry.