Microstructural evolution was examined in annealed 316 stainless steel after heavy-ion bombardment in the range 1 to 256 dpa at 900 K with simultaneously implanted helium at a rate of 10 appm/dpa and deuterium at a rate of 25 appm/dpa. Phase decomposition was rather limited compared with that in neutron irradiations; only an unidentified plate-like precipitate at low dose, and blocky M^{2 3}C⁶ particles on grain boundaries were formed. Swelling from cavity formation increased with dose to about 20% at about 200 dpa above which it appeared to saturate. Cavity concentrations saturated at about 100 dpa, and dislocations much earlier. The matrix cavities included a persistant complement of ∼7-nm diam small cavities. Similar-size helium bubbles were prolific on the grain boundaries.