A full-dimensional quantum dynamical study of vibrational relaxation in H-2 + H-2 collisions using a recently developed potential energy surface of Boothroyd et al. is reported for both ortho- and para-H-2. A comparison of theoretical and experimental rate coefficients is made. The existence of a minimum in rate coefficients as a function of temperature is predicted. (C) 2002 Elsevier Science B.V. All rights reserved.