A detailed study has been made of the void and dislocation microstructure of Types 304 and 316 stainless steel irradiated with 4-MeV ⁵⁸N⁺ at a displacement rate of 5 × 10^-3 dpa/s^-1. The range of dosages investigated were 20 to 350 dpa at 525 C (977 F) and 20 to 250 dpa at 600 C (1112 F) for Type 304 stainless steel and 20 to 250 dpa at 525 C for Type 316. The maximum swelling data for Type 304 stainless steel may be represented by a power-law dependence on-dosage with exponents of 1.4 and 1.8 at 525 and 600 C, respectively. The swelling at 600 C, which is much greater than that at 525 C, is due to the more rapid growth of voids at the higher temperature. No evidence of a reduction in swelling rate at high dosages was found at either temperature. The swelling of Type 316 stainless steel shows a tendency to be lower than that of Type 304 and, at higher dosages, is a factor of two less. In 20 percent cold-worked Type 316 stainless steel, swelling was suppressed until the dislocation structure was recovered.