A new crystalline form and a solvate of glibenclamide were prepared and characterized by hot-stage microscopy, DSC, IR, scanning electron microscope, X-ray powder diffraction and dissolution studies. From I, III and the solvate which melt at 174.4, 153.2 and 109.3 degrees C, were obtained by crystallization. Significant differences between the three forms in the X-ray and IR spectra were observed. Polymorphic transformation was observed for the least stable form (III) to the most stable one (form I) upon storage at different temperatures and trituration. The dissolution profiles showed significant differences between the three forms, with form III having the highest dissolution rate.