A new six-dimensional analytical potential energy surface for the hydrogen bonded dimer (HF)2is presented. It is based on theab initiostudy by Kofraneket al., and uses 1070 points with energies up to 500 kJ mol-1as well as recent correlated dispersion coefficients from a perturbation treatment by Rijks and Wormer, and the experimental Morse parameters for the HF monomer. The fit to theab initiopoints contains 29 free and several constrained parameters and has a weighted standard deviation of 29·5 cm-1. A brief description of some properties of the new surface is given. Preliminary results of a diffusion quantum Monte Carlo (QMC) study for vibrational energy levels on the new surface as well as on a surface published by Bunkeret al.are given. An interesting anharmonic isotope effect in thev6fundamental is discussed and explained.