The microstructure of the low activation F82H ferritic/martensitic steel has been investigated in the cases of the heat treated, irradiated and deformed material. The irradiation has been achieved with 590 MeV protons in the Proton IRradiation EXperiment (PIREX) facility to a dose of 0.5 dpa at a temperature of 523 K. The unirradiated material was deformed in tension to failure at room temperature. The dislocations character as well as the dislocation density are determined. The carbide chemical composition and the size distribution of the carbides are assessed. (C) 1998 Elsevier Science B.V. All rights reserved.