Abstract The nuclear decay properties of the very heavy elements have been examined in order to investigate the apparent instability for nuclides with 158 or more neutrons. The recent data for the energetics and lifetimes of alpha-, beta-, and spontaneous fission-decay are found to be generally consistent with earlier predictions of the author for species with neutron number N = 140–157. For N ⩾ 158 it appears that spontaneous fission instability is much greater than expected from semi-empirical calculations based on a unified nuclear model. This result is interpreted as a possible indication of anomalous behavior in the nuclear level structure of the heaviest nuclei. Also, in the course of this work the Garvey-Kelson mass relationship was studied for use in extending the heavy element mass surface. It was found that this relationship gave results generally consistent with Way-Wood systematics, but was inferior to the latter type of extrapolation because of inconsistencies with the more sensitive systematics of alpha-decay.