Terfenadine was crystallized from solutions of the drug in ethanol, acetone, and methanol. Two polymorphic forms and a methanol solvate were obtained and characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetry (TG). Kinetic parameters were determined for a structural change that the methanol solvate went through during the desolvation reaction which was found to be completed by heating. On the basis of the X-ray diffractogram and the DSC scan the desolvated product was identified as the lower melting polymorph.