The effect of crystallisation solvent on crystal morphology and mechanical properties of ibuprofen was studied. Intermolecular potentials were calculated to assess the relative growth rates of crystal faces of ibuprofen. Comparison of the predicted morphology with solution-"grown crystals clarified the interaction of solvent with the growing crystal. Single crystal dissolution and x--ray techniques indicated that crystals grown from non--polar solvents were more strained. In conjunction with solution NMR results (which showed differences in molecular association in solvents of varying polarity) this led to two different growth mechanisms being proposed. The crystal structure of resolved S(+) ibuprofen confirmed that enantiomeric dimers present in non-polar solvents could act as additives, selectively decreasing the growth rate at specific crystal faces, and introducing lattice strain. Deformation processes of ibuprofen did not appear to be changed by the solvent of crystallisation. However, crystals grown from non-polar solvents fractured readily. In conjunction with the unfavourable acicular morphology this is likely to be a source of processing problems of industrially produced crystals.