The amino acid DL-norvaline undergoes two solid-solid phase transitions between room temperature and -180 degrees C. Single-Crystal X-ray diffraction studies show that the first of these transitions, taking place around -80 degrees C, is completely reversible with respect to crystal quality, whereas the second, taking place below -100 degrees C, is not due to crystal delamination. High-quality crystal structures were obtained for the higher temperature phase beta (at -70 degrees C) and the intermediate temperature phase alpha (at -90 degrees C). They show that although side-chain disorder is present for both forms, the beta-to-alpha phase transition induces significant side-chain rearrangements, which are accompanied by a substantial reduction in molecular volume. The observed polymorphs are compared with those found for DL-aminobutyric acid, DL-norleucine, and DL-methionine.