The two chiral isomers of the surfactant (+/-)-2-dodecyl beta-D-glucoside have been prepared, and their thermotropic and lyotropic liquid crystalline behavior has been studied. Mixtures of the two pure diastereomers were prepared in known ratios to examine the effect of chiral purity on these properties using the techniques of differential scanning calorimetry and polarized light optical microscopy. It was found that the (+/-)-diastereomer produced crystalline and liquid crystalline phases in the presence and absence of water, which were more thermally stable than the (-)-diastereomer. The transition temperatures were reduced with increasing amounts of the (-)-diastereomer, but eutectic-like behavior was not exhibited, indicating metastable cosolubility. The large differences in thermotropic and lyotropic phase behavior may be due to the gross changes in molecular shape resulting from the very subtle difference in structure. This change in shape is likely to affect the molecular packing and headgroup interactions that stabilize the crystalline and liquid crystalline phases in other glucose-based surfactants.