Optical second harmonic generation (SHG) studies of malachite green (MG) adsorbed at the fused-silica/air interface have been conducted. The concentration dependence of the second harmonic intensity indicates the formation of ordered monolayers normal to the interface. Polarization SHG experiments have been used to extract the averaged molecular orientation in adjacent molecular layers and to characterize the breadth of the orientation distribution. MG adsorbs in an upright orientation with its molecular plane near normal to the surface. This orientation is consistent with the interaction of the polar surface and the polar dimethylamino substituents of the adsorbate. Molecular orientation in the second monolayer resembles that in the first, but also reflects some additional broadening of the orientation distribution function. The onset of parallel, sandwich-type aggregates has been observed within the first monolayer. The formation of parallel, sandwich-type, intralayer aggregates is distinct from the interlayer aggregation observed between adjacent monolayers of rhodamine 6G. These differences result from the nature of the molecule-surface interactions that define their respective orientations in the first monolayer. Thus, it appears that the order observed in these ultrathin organic films is dictated by the molecule-surface interactions within the first monolayer as well as the magnitude of the intermolecular interactions in subsequent layers.