The energies, lifetimes and product state distributions for vibrational predissociation of the van der Waals complex (C2H4)2 have been calculated. A coupled channel method, which includes both vibration and azimuthal rotation of the ethylene monomers, has been used. Lifetimes are found to be of the order of 10–6 s, which supports the recent observation by Snels et al. that fine structure exists within the infrared photodissociation spectrum. A curve-crossing mechanism propsed by Ewing is also investigated but cannot account for lifetimes on the picosecond timescale.