Novel crystalline forms of (2R,3S,5R)-2-(2,5-Difluorophenyl)-5-[2-(methylsulfonyl)-2,6-dihydropyrrolo[3,4-c]pyrazol-5(4H)-yl]tetrahydro-2H-pyran-3-amine are potent inhibitors of dipeptidyl peptidase-IV and are useful for the treatment of non-insulin dependent (Type 2) diabetes mellitus. The invention also relates to pharmaceutical compositions containing these novel forms, processes to prepare these forms and their pharmaceutical compositions as well as uses thereof for the treatment of Type 2 diabetes.